forked from OSchip/llvm-project
938 lines
26 KiB
Plaintext
938 lines
26 KiB
Plaintext
//===---------------------------------------------------------------------===//
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// Random ideas for the X86 backend: SSE-specific stuff.
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//===---------------------------------------------------------------------===//
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//===---------------------------------------------------------------------===//
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SSE Variable shift can be custom lowered to something like this, which uses a
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small table + unaligned load + shuffle instead of going through memory.
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__m128i_shift_right:
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.byte 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15
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.byte -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1
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...
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__m128i shift_right(__m128i value, unsigned long offset) {
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return _mm_shuffle_epi8(value,
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_mm_loadu_si128((__m128 *) (___m128i_shift_right + offset)));
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}
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//===---------------------------------------------------------------------===//
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SSE has instructions for doing operations on complex numbers, we should pattern
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match them. For example, this should turn into a horizontal add:
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typedef float __attribute__((vector_size(16))) v4f32;
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float f32(v4f32 A) {
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return A[0]+A[1]+A[2]+A[3];
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}
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Instead we get this:
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_f32: ## @f32
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pshufd $1, %xmm0, %xmm1 ## xmm1 = xmm0[1,0,0,0]
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addss %xmm0, %xmm1
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pshufd $3, %xmm0, %xmm2 ## xmm2 = xmm0[3,0,0,0]
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movhlps %xmm0, %xmm0 ## xmm0 = xmm0[1,1]
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movaps %xmm0, %xmm3
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addss %xmm1, %xmm3
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movdqa %xmm2, %xmm0
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addss %xmm3, %xmm0
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ret
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Also, there are cases where some simple local SLP would improve codegen a bit.
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compiling this:
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_Complex float f32(_Complex float A, _Complex float B) {
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return A+B;
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}
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into:
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_f32: ## @f32
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movdqa %xmm0, %xmm2
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addss %xmm1, %xmm2
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pshufd $1, %xmm1, %xmm1 ## xmm1 = xmm1[1,0,0,0]
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pshufd $1, %xmm0, %xmm3 ## xmm3 = xmm0[1,0,0,0]
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addss %xmm1, %xmm3
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movaps %xmm2, %xmm0
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unpcklps %xmm3, %xmm0 ## xmm0 = xmm0[0],xmm3[0],xmm0[1],xmm3[1]
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ret
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seems silly when it could just be one addps.
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//===---------------------------------------------------------------------===//
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Expand libm rounding functions inline: Significant speedups possible.
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http://gcc.gnu.org/ml/gcc-patches/2006-10/msg00909.html
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//===---------------------------------------------------------------------===//
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When compiled with unsafemath enabled, "main" should enable SSE DAZ mode and
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other fast SSE modes.
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//===---------------------------------------------------------------------===//
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Think about doing i64 math in SSE regs on x86-32.
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//===---------------------------------------------------------------------===//
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This testcase should have no SSE instructions in it, and only one load from
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a constant pool:
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double %test3(bool %B) {
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%C = select bool %B, double 123.412, double 523.01123123
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ret double %C
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}
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Currently, the select is being lowered, which prevents the dag combiner from
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turning 'select (load CPI1), (load CPI2)' -> 'load (select CPI1, CPI2)'
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The pattern isel got this one right.
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//===---------------------------------------------------------------------===//
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SSE should implement 'select_cc' using 'emulated conditional moves' that use
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pcmp/pand/pandn/por to do a selection instead of a conditional branch:
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double %X(double %Y, double %Z, double %A, double %B) {
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%C = setlt double %A, %B
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%z = fadd double %Z, 0.0 ;; select operand is not a load
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%D = select bool %C, double %Y, double %z
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ret double %D
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}
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We currently emit:
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_X:
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subl $12, %esp
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xorpd %xmm0, %xmm0
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addsd 24(%esp), %xmm0
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movsd 32(%esp), %xmm1
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movsd 16(%esp), %xmm2
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ucomisd 40(%esp), %xmm1
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jb LBB_X_2
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LBB_X_1:
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movsd %xmm0, %xmm2
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LBB_X_2:
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movsd %xmm2, (%esp)
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fldl (%esp)
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addl $12, %esp
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ret
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//===---------------------------------------------------------------------===//
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Lower memcpy / memset to a series of SSE 128 bit move instructions when it's
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feasible.
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//===---------------------------------------------------------------------===//
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Codegen:
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if (copysign(1.0, x) == copysign(1.0, y))
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into:
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if (x^y & mask)
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when using SSE.
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//===---------------------------------------------------------------------===//
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Use movhps to update upper 64-bits of a v4sf value. Also movlps on lower half
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of a v4sf value.
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//===---------------------------------------------------------------------===//
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Better codegen for vector_shuffles like this { x, 0, 0, 0 } or { x, 0, x, 0}.
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Perhaps use pxor / xorp* to clear a XMM register first?
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//===---------------------------------------------------------------------===//
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External test Nurbs exposed some problems. Look for
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__ZN15Nurbs_SSE_Cubic17TessellateSurfaceE, bb cond_next140. This is what icc
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emits:
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movaps (%edx), %xmm2 #59.21
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movaps (%edx), %xmm5 #60.21
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movaps (%edx), %xmm4 #61.21
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movaps (%edx), %xmm3 #62.21
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movl 40(%ecx), %ebp #69.49
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shufps $0, %xmm2, %xmm5 #60.21
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movl 100(%esp), %ebx #69.20
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movl (%ebx), %edi #69.20
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imull %ebp, %edi #69.49
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addl (%eax), %edi #70.33
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shufps $85, %xmm2, %xmm4 #61.21
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shufps $170, %xmm2, %xmm3 #62.21
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shufps $255, %xmm2, %xmm2 #63.21
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lea (%ebp,%ebp,2), %ebx #69.49
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negl %ebx #69.49
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lea -3(%edi,%ebx), %ebx #70.33
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shll $4, %ebx #68.37
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addl 32(%ecx), %ebx #68.37
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testb $15, %bl #91.13
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jne L_B1.24 # Prob 5% #91.13
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This is the llvm code after instruction scheduling:
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cond_next140 (0xa910740, LLVM BB @0xa90beb0):
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%reg1078 = MOV32ri -3
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%reg1079 = ADD32rm %reg1078, %reg1068, 1, %NOREG, 0
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%reg1037 = MOV32rm %reg1024, 1, %NOREG, 40
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%reg1080 = IMUL32rr %reg1079, %reg1037
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%reg1081 = MOV32rm %reg1058, 1, %NOREG, 0
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%reg1038 = LEA32r %reg1081, 1, %reg1080, -3
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%reg1036 = MOV32rm %reg1024, 1, %NOREG, 32
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%reg1082 = SHL32ri %reg1038, 4
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%reg1039 = ADD32rr %reg1036, %reg1082
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%reg1083 = MOVAPSrm %reg1059, 1, %NOREG, 0
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%reg1034 = SHUFPSrr %reg1083, %reg1083, 170
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%reg1032 = SHUFPSrr %reg1083, %reg1083, 0
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%reg1035 = SHUFPSrr %reg1083, %reg1083, 255
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%reg1033 = SHUFPSrr %reg1083, %reg1083, 85
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%reg1040 = MOV32rr %reg1039
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%reg1084 = AND32ri8 %reg1039, 15
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CMP32ri8 %reg1084, 0
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JE mbb<cond_next204,0xa914d30>
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Still ok. After register allocation:
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cond_next140 (0xa910740, LLVM BB @0xa90beb0):
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%EAX = MOV32ri -3
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%EDX = MOV32rm <fi#3>, 1, %NOREG, 0
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ADD32rm %EAX<def&use>, %EDX, 1, %NOREG, 0
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%EDX = MOV32rm <fi#7>, 1, %NOREG, 0
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%EDX = MOV32rm %EDX, 1, %NOREG, 40
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IMUL32rr %EAX<def&use>, %EDX
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%ESI = MOV32rm <fi#5>, 1, %NOREG, 0
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%ESI = MOV32rm %ESI, 1, %NOREG, 0
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MOV32mr <fi#4>, 1, %NOREG, 0, %ESI
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%EAX = LEA32r %ESI, 1, %EAX, -3
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%ESI = MOV32rm <fi#7>, 1, %NOREG, 0
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%ESI = MOV32rm %ESI, 1, %NOREG, 32
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%EDI = MOV32rr %EAX
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SHL32ri %EDI<def&use>, 4
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ADD32rr %EDI<def&use>, %ESI
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%XMM0 = MOVAPSrm %ECX, 1, %NOREG, 0
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%XMM1 = MOVAPSrr %XMM0
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SHUFPSrr %XMM1<def&use>, %XMM1, 170
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%XMM2 = MOVAPSrr %XMM0
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SHUFPSrr %XMM2<def&use>, %XMM2, 0
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%XMM3 = MOVAPSrr %XMM0
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SHUFPSrr %XMM3<def&use>, %XMM3, 255
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SHUFPSrr %XMM0<def&use>, %XMM0, 85
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%EBX = MOV32rr %EDI
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AND32ri8 %EBX<def&use>, 15
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CMP32ri8 %EBX, 0
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JE mbb<cond_next204,0xa914d30>
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This looks really bad. The problem is shufps is a destructive opcode. Since it
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appears as operand two in more than one shufps ops. It resulted in a number of
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copies. Note icc also suffers from the same problem. Either the instruction
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selector should select pshufd or The register allocator can made the two-address
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to three-address transformation.
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It also exposes some other problems. See MOV32ri -3 and the spills.
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//===---------------------------------------------------------------------===//
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Consider:
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__m128 test(float a) {
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return _mm_set_ps(0.0, 0.0, 0.0, a*a);
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}
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This compiles into:
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movss 4(%esp), %xmm1
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mulss %xmm1, %xmm1
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xorps %xmm0, %xmm0
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movss %xmm1, %xmm0
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ret
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Because mulss doesn't modify the top 3 elements, the top elements of
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xmm1 are already zero'd. We could compile this to:
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movss 4(%esp), %xmm0
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mulss %xmm0, %xmm0
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ret
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//===---------------------------------------------------------------------===//
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Here's a sick and twisted idea. Consider code like this:
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__m128 test(__m128 a) {
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float b = *(float*)&A;
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...
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return _mm_set_ps(0.0, 0.0, 0.0, b);
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}
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This might compile to this code:
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movaps c(%esp), %xmm1
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xorps %xmm0, %xmm0
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movss %xmm1, %xmm0
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ret
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Now consider if the ... code caused xmm1 to get spilled. This might produce
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this code:
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movaps c(%esp), %xmm1
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movaps %xmm1, c2(%esp)
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...
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xorps %xmm0, %xmm0
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movaps c2(%esp), %xmm1
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movss %xmm1, %xmm0
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ret
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However, since the reload is only used by these instructions, we could
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"fold" it into the uses, producing something like this:
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movaps c(%esp), %xmm1
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movaps %xmm1, c2(%esp)
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...
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movss c2(%esp), %xmm0
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ret
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... saving two instructions.
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The basic idea is that a reload from a spill slot, can, if only one 4-byte
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chunk is used, bring in 3 zeros the one element instead of 4 elements.
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This can be used to simplify a variety of shuffle operations, where the
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elements are fixed zeros.
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//===---------------------------------------------------------------------===//
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This code generates ugly code, probably due to costs being off or something:
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define void @test(float* %P, <4 x float>* %P2 ) {
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%xFloat0.688 = load float* %P
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%tmp = load <4 x float>* %P2
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%inFloat3.713 = insertelement <4 x float> %tmp, float 0.0, i32 3
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store <4 x float> %inFloat3.713, <4 x float>* %P2
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ret void
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}
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Generates:
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_test:
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movl 8(%esp), %eax
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movaps (%eax), %xmm0
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pxor %xmm1, %xmm1
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movaps %xmm0, %xmm2
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shufps $50, %xmm1, %xmm2
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shufps $132, %xmm2, %xmm0
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movaps %xmm0, (%eax)
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ret
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Would it be better to generate:
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_test:
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movl 8(%esp), %ecx
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movaps (%ecx), %xmm0
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xor %eax, %eax
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pinsrw $6, %eax, %xmm0
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pinsrw $7, %eax, %xmm0
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movaps %xmm0, (%ecx)
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ret
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?
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//===---------------------------------------------------------------------===//
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Some useful information in the Apple Altivec / SSE Migration Guide:
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http://developer.apple.com/documentation/Performance/Conceptual/
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Accelerate_sse_migration/index.html
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e.g. SSE select using and, andnot, or. Various SSE compare translations.
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//===---------------------------------------------------------------------===//
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Add hooks to commute some CMPP operations.
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//===---------------------------------------------------------------------===//
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Apply the same transformation that merged four float into a single 128-bit load
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to loads from constant pool.
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//===---------------------------------------------------------------------===//
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Floating point max / min are commutable when -enable-unsafe-fp-path is
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specified. We should turn int_x86_sse_max_ss and X86ISD::FMIN etc. into other
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nodes which are selected to max / min instructions that are marked commutable.
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//===---------------------------------------------------------------------===//
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We should materialize vector constants like "all ones" and "signbit" with
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code like:
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cmpeqps xmm1, xmm1 ; xmm1 = all-ones
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and:
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cmpeqps xmm1, xmm1 ; xmm1 = all-ones
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psrlq xmm1, 31 ; xmm1 = all 100000000000...
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instead of using a load from the constant pool. The later is important for
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ABS/NEG/copysign etc.
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//===---------------------------------------------------------------------===//
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These functions:
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#include <xmmintrin.h>
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__m128i a;
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void x(unsigned short n) {
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a = _mm_slli_epi32 (a, n);
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}
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void y(unsigned n) {
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a = _mm_slli_epi32 (a, n);
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}
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compile to ( -O3 -static -fomit-frame-pointer):
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_x:
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movzwl 4(%esp), %eax
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movd %eax, %xmm0
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movaps _a, %xmm1
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pslld %xmm0, %xmm1
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movaps %xmm1, _a
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ret
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_y:
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movd 4(%esp), %xmm0
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movaps _a, %xmm1
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pslld %xmm0, %xmm1
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movaps %xmm1, _a
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ret
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"y" looks good, but "x" does silly movzwl stuff around into a GPR. It seems
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like movd would be sufficient in both cases as the value is already zero
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extended in the 32-bit stack slot IIRC. For signed short, it should also be
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save, as a really-signed value would be undefined for pslld.
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//===---------------------------------------------------------------------===//
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#include <math.h>
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int t1(double d) { return signbit(d); }
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This currently compiles to:
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subl $12, %esp
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movsd 16(%esp), %xmm0
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movsd %xmm0, (%esp)
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movl 4(%esp), %eax
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shrl $31, %eax
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addl $12, %esp
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ret
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We should use movmskp{s|d} instead.
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//===---------------------------------------------------------------------===//
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CodeGen/X86/vec_align.ll tests whether we can turn 4 scalar loads into a single
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(aligned) vector load. This functionality has a couple of problems.
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1. The code to infer alignment from loads of globals is in the X86 backend,
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not the dag combiner. This is because dagcombine2 needs to be able to see
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through the X86ISD::Wrapper node, which DAGCombine can't really do.
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2. The code for turning 4 x load into a single vector load is target
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independent and should be moved to the dag combiner.
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3. The code for turning 4 x load into a vector load can only handle a direct
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load from a global or a direct load from the stack. It should be generalized
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to handle any load from P, P+4, P+8, P+12, where P can be anything.
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4. The alignment inference code cannot handle loads from globals in non-static
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mode because it doesn't look through the extra dyld stub load. If you try
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vec_align.ll without -relocation-model=static, you'll see what I mean.
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//===---------------------------------------------------------------------===//
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We should lower store(fneg(load p), q) into an integer load+xor+store, which
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eliminates a constant pool load. For example, consider:
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define i64 @ccosf(float %z.0, float %z.1) nounwind readonly {
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entry:
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%tmp6 = fsub float -0.000000e+00, %z.1 ; <float> [#uses=1]
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%tmp20 = tail call i64 @ccoshf( float %tmp6, float %z.0 ) nounwind readonly
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ret i64 %tmp20
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}
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declare i64 @ccoshf(float %z.0, float %z.1) nounwind readonly
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This currently compiles to:
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LCPI1_0: # <4 x float>
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.long 2147483648 # float -0
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.long 2147483648 # float -0
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.long 2147483648 # float -0
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.long 2147483648 # float -0
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_ccosf:
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subl $12, %esp
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movss 16(%esp), %xmm0
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movss %xmm0, 4(%esp)
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movss 20(%esp), %xmm0
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xorps LCPI1_0, %xmm0
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movss %xmm0, (%esp)
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call L_ccoshf$stub
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addl $12, %esp
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ret
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Note the load into xmm0, then xor (to negate), then store. In PIC mode,
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this code computes the pic base and does two loads to do the constant pool
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load, so the improvement is much bigger.
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The tricky part about this xform is that the argument load/store isn't exposed
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until post-legalize, and at that point, the fneg has been custom expanded into
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an X86 fxor. This means that we need to handle this case in the x86 backend
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instead of in target independent code.
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//===---------------------------------------------------------------------===//
|
|
|
|
Non-SSE4 insert into 16 x i8 is atrociously bad.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
<2 x i64> extract is substantially worse than <2 x f64>, even if the destination
|
|
is memory.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
SSE4 extract-to-mem ops aren't being pattern matched because of the AssertZext
|
|
sitting between the truncate and the extract.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
INSERTPS can match any insert (extract, imm1), imm2 for 4 x float, and insert
|
|
any number of 0.0 simultaneously. Currently we only use it for simple
|
|
insertions.
|
|
|
|
See comments in LowerINSERT_VECTOR_ELT_SSE4.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
On a random note, SSE2 should declare insert/extract of 2 x f64 as legal, not
|
|
Custom. All combinations of insert/extract reg-reg, reg-mem, and mem-reg are
|
|
legal, it'll just take a few extra patterns written in the .td file.
|
|
|
|
Note: this is not a code quality issue; the custom lowered code happens to be
|
|
right, but we shouldn't have to custom lower anything. This is probably related
|
|
to <2 x i64> ops being so bad.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
'select' on vectors and scalars could be a whole lot better. We currently
|
|
lower them to conditional branches. On x86-64 for example, we compile this:
|
|
|
|
double test(double a, double b, double c, double d) { return a<b ? c : d; }
|
|
|
|
to:
|
|
|
|
_test:
|
|
ucomisd %xmm0, %xmm1
|
|
ja LBB1_2 # entry
|
|
LBB1_1: # entry
|
|
movapd %xmm3, %xmm2
|
|
LBB1_2: # entry
|
|
movapd %xmm2, %xmm0
|
|
ret
|
|
|
|
instead of:
|
|
|
|
_test:
|
|
cmpltsd %xmm1, %xmm0
|
|
andpd %xmm0, %xmm2
|
|
andnpd %xmm3, %xmm0
|
|
orpd %xmm2, %xmm0
|
|
ret
|
|
|
|
For unpredictable branches, the later is much more efficient. This should
|
|
just be a matter of having scalar sse map to SELECT_CC and custom expanding
|
|
or iseling it.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
LLVM currently generates stack realignment code, when it is not necessary
|
|
needed. The problem is that we need to know about stack alignment too early,
|
|
before RA runs.
|
|
|
|
At that point we don't know, whether there will be vector spill, or not.
|
|
Stack realignment logic is overly conservative here, but otherwise we can
|
|
produce unaligned loads/stores.
|
|
|
|
Fixing this will require some huge RA changes.
|
|
|
|
Testcase:
|
|
#include <emmintrin.h>
|
|
|
|
typedef short vSInt16 __attribute__ ((__vector_size__ (16)));
|
|
|
|
static const vSInt16 a = {- 22725, - 12873, - 22725, - 12873, - 22725, - 12873,
|
|
- 22725, - 12873};;
|
|
|
|
vSInt16 madd(vSInt16 b)
|
|
{
|
|
return _mm_madd_epi16(a, b);
|
|
}
|
|
|
|
Generated code (x86-32, linux):
|
|
madd:
|
|
pushl %ebp
|
|
movl %esp, %ebp
|
|
andl $-16, %esp
|
|
movaps .LCPI1_0, %xmm1
|
|
pmaddwd %xmm1, %xmm0
|
|
movl %ebp, %esp
|
|
popl %ebp
|
|
ret
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Consider:
|
|
#include <emmintrin.h>
|
|
__m128 foo2 (float x) {
|
|
return _mm_set_ps (0, 0, x, 0);
|
|
}
|
|
|
|
In x86-32 mode, we generate this spiffy code:
|
|
|
|
_foo2:
|
|
movss 4(%esp), %xmm0
|
|
pshufd $81, %xmm0, %xmm0
|
|
ret
|
|
|
|
in x86-64 mode, we generate this code, which could be better:
|
|
|
|
_foo2:
|
|
xorps %xmm1, %xmm1
|
|
movss %xmm0, %xmm1
|
|
pshufd $81, %xmm1, %xmm0
|
|
ret
|
|
|
|
In sse4 mode, we could use insertps to make both better.
|
|
|
|
Here's another testcase that could use insertps [mem]:
|
|
|
|
#include <xmmintrin.h>
|
|
extern float x2, x3;
|
|
__m128 foo1 (float x1, float x4) {
|
|
return _mm_set_ps (x2, x1, x3, x4);
|
|
}
|
|
|
|
gcc mainline compiles it to:
|
|
|
|
foo1:
|
|
insertps $0x10, x2(%rip), %xmm0
|
|
insertps $0x10, x3(%rip), %xmm1
|
|
movaps %xmm1, %xmm2
|
|
movlhps %xmm0, %xmm2
|
|
movaps %xmm2, %xmm0
|
|
ret
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We compile vector multiply-by-constant into poor code:
|
|
|
|
define <4 x i32> @f(<4 x i32> %i) nounwind {
|
|
%A = mul <4 x i32> %i, < i32 10, i32 10, i32 10, i32 10 >
|
|
ret <4 x i32> %A
|
|
}
|
|
|
|
On targets without SSE4.1, this compiles into:
|
|
|
|
LCPI1_0: ## <4 x i32>
|
|
.long 10
|
|
.long 10
|
|
.long 10
|
|
.long 10
|
|
.text
|
|
.align 4,0x90
|
|
.globl _f
|
|
_f:
|
|
pshufd $3, %xmm0, %xmm1
|
|
movd %xmm1, %eax
|
|
imull LCPI1_0+12, %eax
|
|
movd %eax, %xmm1
|
|
pshufd $1, %xmm0, %xmm2
|
|
movd %xmm2, %eax
|
|
imull LCPI1_0+4, %eax
|
|
movd %eax, %xmm2
|
|
punpckldq %xmm1, %xmm2
|
|
movd %xmm0, %eax
|
|
imull LCPI1_0, %eax
|
|
movd %eax, %xmm1
|
|
movhlps %xmm0, %xmm0
|
|
movd %xmm0, %eax
|
|
imull LCPI1_0+8, %eax
|
|
movd %eax, %xmm0
|
|
punpckldq %xmm0, %xmm1
|
|
movaps %xmm1, %xmm0
|
|
punpckldq %xmm2, %xmm0
|
|
ret
|
|
|
|
It would be better to synthesize integer vector multiplication by constants
|
|
using shifts and adds, pslld and paddd here. And even on targets with SSE4.1,
|
|
simple cases such as multiplication by powers of two would be better as
|
|
vector shifts than as multiplications.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We compile this:
|
|
|
|
__m128i
|
|
foo2 (char x)
|
|
{
|
|
return _mm_set_epi8 (1, 0, 0, 0, 0, 0, 0, 0, 0, x, 0, 1, 0, 0, 0, 0);
|
|
}
|
|
|
|
into:
|
|
movl $1, %eax
|
|
xorps %xmm0, %xmm0
|
|
pinsrw $2, %eax, %xmm0
|
|
movzbl 4(%esp), %eax
|
|
pinsrw $3, %eax, %xmm0
|
|
movl $256, %eax
|
|
pinsrw $7, %eax, %xmm0
|
|
ret
|
|
|
|
|
|
gcc-4.2:
|
|
subl $12, %esp
|
|
movzbl 16(%esp), %eax
|
|
movdqa LC0, %xmm0
|
|
pinsrw $3, %eax, %xmm0
|
|
addl $12, %esp
|
|
ret
|
|
.const
|
|
.align 4
|
|
LC0:
|
|
.word 0
|
|
.word 0
|
|
.word 1
|
|
.word 0
|
|
.word 0
|
|
.word 0
|
|
.word 0
|
|
.word 256
|
|
|
|
With SSE4, it should be
|
|
movdqa .LC0(%rip), %xmm0
|
|
pinsrb $6, %edi, %xmm0
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We should transform a shuffle of two vectors of constants into a single vector
|
|
of constants. Also, insertelement of a constant into a vector of constants
|
|
should also result in a vector of constants. e.g. 2008-06-25-VecISelBug.ll.
|
|
|
|
We compiled it to something horrible:
|
|
|
|
.align 4
|
|
LCPI1_1: ## float
|
|
.long 1065353216 ## float 1
|
|
.const
|
|
|
|
.align 4
|
|
LCPI1_0: ## <4 x float>
|
|
.space 4
|
|
.long 1065353216 ## float 1
|
|
.space 4
|
|
.long 1065353216 ## float 1
|
|
.text
|
|
.align 4,0x90
|
|
.globl _t
|
|
_t:
|
|
xorps %xmm0, %xmm0
|
|
movhps LCPI1_0, %xmm0
|
|
movss LCPI1_1, %xmm1
|
|
movaps %xmm0, %xmm2
|
|
shufps $2, %xmm1, %xmm2
|
|
shufps $132, %xmm2, %xmm0
|
|
movaps %xmm0, 0
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
rdar://5907648
|
|
|
|
This function:
|
|
|
|
float foo(unsigned char x) {
|
|
return x;
|
|
}
|
|
|
|
compiles to (x86-32):
|
|
|
|
define float @foo(i8 zeroext %x) nounwind {
|
|
%tmp12 = uitofp i8 %x to float ; <float> [#uses=1]
|
|
ret float %tmp12
|
|
}
|
|
|
|
compiles to:
|
|
|
|
_foo:
|
|
subl $4, %esp
|
|
movzbl 8(%esp), %eax
|
|
cvtsi2ss %eax, %xmm0
|
|
movss %xmm0, (%esp)
|
|
flds (%esp)
|
|
addl $4, %esp
|
|
ret
|
|
|
|
We should be able to use:
|
|
cvtsi2ss 8($esp), %xmm0
|
|
since we know the stack slot is already zext'd.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Consider using movlps instead of movsd to implement (scalar_to_vector (loadf64))
|
|
when code size is critical. movlps is slower than movsd on core2 but it's one
|
|
byte shorter.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We should use a dynamic programming based approach to tell when using FPStack
|
|
operations is cheaper than SSE. SciMark montecarlo contains code like this
|
|
for example:
|
|
|
|
double MonteCarlo_num_flops(int Num_samples) {
|
|
return ((double) Num_samples)* 4.0;
|
|
}
|
|
|
|
In fpstack mode, this compiles into:
|
|
|
|
LCPI1_0:
|
|
.long 1082130432 ## float 4.000000e+00
|
|
_MonteCarlo_num_flops:
|
|
subl $4, %esp
|
|
movl 8(%esp), %eax
|
|
movl %eax, (%esp)
|
|
fildl (%esp)
|
|
fmuls LCPI1_0
|
|
addl $4, %esp
|
|
ret
|
|
|
|
in SSE mode, it compiles into significantly slower code:
|
|
|
|
_MonteCarlo_num_flops:
|
|
subl $12, %esp
|
|
cvtsi2sd 16(%esp), %xmm0
|
|
mulsd LCPI1_0, %xmm0
|
|
movsd %xmm0, (%esp)
|
|
fldl (%esp)
|
|
addl $12, %esp
|
|
ret
|
|
|
|
There are also other cases in scimark where using fpstack is better, it is
|
|
cheaper to do fld1 than load from a constant pool for example, so
|
|
"load, add 1.0, store" is better done in the fp stack, etc.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
The X86 backend should be able to if-convert SSE comparisons like "ucomisd" to
|
|
"cmpsd". For example, this code:
|
|
|
|
double d1(double x) { return x == x ? x : x + x; }
|
|
|
|
Compiles into:
|
|
|
|
_d1:
|
|
ucomisd %xmm0, %xmm0
|
|
jnp LBB1_2
|
|
addsd %xmm0, %xmm0
|
|
ret
|
|
LBB1_2:
|
|
ret
|
|
|
|
Also, the 'ret's should be shared. This is PR6032.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
These should compile into the same code (PR6214): Perhaps instcombine should
|
|
canonicalize the former into the later?
|
|
|
|
define float @foo(float %x) nounwind {
|
|
%t = bitcast float %x to i32
|
|
%s = and i32 %t, 2147483647
|
|
%d = bitcast i32 %s to float
|
|
ret float %d
|
|
}
|
|
|
|
declare float @fabsf(float %n)
|
|
define float @bar(float %x) nounwind {
|
|
%d = call float @fabsf(float %x)
|
|
ret float %d
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
This IR (from PR6194):
|
|
|
|
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
|
|
target triple = "x86_64-apple-darwin10.0.0"
|
|
|
|
%0 = type { double, double }
|
|
%struct.float3 = type { float, float, float }
|
|
|
|
define void @test(%0, %struct.float3* nocapture %res) nounwind noinline ssp {
|
|
entry:
|
|
%tmp18 = extractvalue %0 %0, 0 ; <double> [#uses=1]
|
|
%tmp19 = bitcast double %tmp18 to i64 ; <i64> [#uses=1]
|
|
%tmp20 = zext i64 %tmp19 to i128 ; <i128> [#uses=1]
|
|
%tmp10 = lshr i128 %tmp20, 32 ; <i128> [#uses=1]
|
|
%tmp11 = trunc i128 %tmp10 to i32 ; <i32> [#uses=1]
|
|
%tmp12 = bitcast i32 %tmp11 to float ; <float> [#uses=1]
|
|
%tmp5 = getelementptr inbounds %struct.float3* %res, i64 0, i32 1 ; <float*> [#uses=1]
|
|
store float %tmp12, float* %tmp5
|
|
ret void
|
|
}
|
|
|
|
Compiles to:
|
|
|
|
_test: ## @test
|
|
movd %xmm0, %rax
|
|
shrq $32, %rax
|
|
movl %eax, 4(%rdi)
|
|
ret
|
|
|
|
This would be better kept in the SSE unit by treating XMM0 as a 4xfloat and
|
|
doing a shuffle from v[1] to v[0] then a float store.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
On SSE4 machines, we compile this code:
|
|
|
|
define <2 x float> @test2(<2 x float> %Q, <2 x float> %R,
|
|
<2 x float> *%P) nounwind {
|
|
%Z = fadd <2 x float> %Q, %R
|
|
|
|
store <2 x float> %Z, <2 x float> *%P
|
|
ret <2 x float> %Z
|
|
}
|
|
|
|
into:
|
|
|
|
_test2: ## @test2
|
|
## BB#0:
|
|
insertps $0, %xmm2, %xmm2
|
|
insertps $16, %xmm3, %xmm2
|
|
insertps $0, %xmm0, %xmm3
|
|
insertps $16, %xmm1, %xmm3
|
|
addps %xmm2, %xmm3
|
|
movq %xmm3, (%rdi)
|
|
movaps %xmm3, %xmm0
|
|
pshufd $1, %xmm3, %xmm1
|
|
## kill: XMM1<def> XMM1<kill>
|
|
ret
|
|
|
|
The insertps's of $0 are pointless complex copies.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
If SSE4.1 is available we should inline rounding functions instead of emitting
|
|
a libcall.
|
|
|
|
floor: roundsd $0x01, %xmm, %xmm
|
|
ceil: roundsd $0x02, %xmm, %xmm
|
|
|
|
and likewise for the single precision versions.
|
|
|
|
Currently, SelectionDAGBuilder doesn't turn calls to these functions into the
|
|
corresponding nodes and some targets (including X86) aren't ready for them.
|
|
|
|
//===---------------------------------------------------------------------===//
|