forked from OSchip/llvm-project
910 lines
26 KiB
Plaintext
910 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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- Consider eliminating the unaligned SSE load intrinsics, replacing them with
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unaligned LLVM load instructions.
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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 doesn't have [mem] op= reg instructions. If we have an SSE instruction
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like this:
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X += y
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and the register allocator decides to spill X, it is cheaper to emit this as:
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Y += [xslot]
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store Y -> [xslot]
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than as:
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tmp = [xslot]
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tmp += y
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store tmp -> [xslot]
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..and this uses one fewer register (so this should be done at load folding
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time, not at spiller time). *Note* however that this can only be done
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if Y is dead. Here's a testcase:
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@.str_3 = external global [15 x i8]
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declare void @printf(i32, ...)
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define void @main() {
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build_tree.exit:
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br label %no_exit.i7
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no_exit.i7: ; preds = %no_exit.i7, %build_tree.exit
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%tmp.0.1.0.i9 = phi double [ 0.000000e+00, %build_tree.exit ],
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[ %tmp.34.i18, %no_exit.i7 ]
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%tmp.0.0.0.i10 = phi double [ 0.000000e+00, %build_tree.exit ],
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[ %tmp.28.i16, %no_exit.i7 ]
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%tmp.28.i16 = add double %tmp.0.0.0.i10, 0.000000e+00
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%tmp.34.i18 = add double %tmp.0.1.0.i9, 0.000000e+00
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br i1 false, label %Compute_Tree.exit23, label %no_exit.i7
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Compute_Tree.exit23: ; preds = %no_exit.i7
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tail call void (i32, ...)* @printf( i32 0 )
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store double %tmp.34.i18, double* null
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ret void
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}
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We currently emit:
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.BBmain_1:
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xorpd %XMM1, %XMM1
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addsd %XMM0, %XMM1
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*** movsd %XMM2, QWORD PTR [%ESP + 8]
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*** addsd %XMM2, %XMM1
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*** movsd QWORD PTR [%ESP + 8], %XMM2
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jmp .BBmain_1 # no_exit.i7
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This is a bugpoint reduced testcase, which is why the testcase doesn't make
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much sense (e.g. its an infinite loop). :)
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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 = add 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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It's not clear whether we should use pxor or xorps / xorpd to clear XMM
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registers. The choice may depend on subtarget information. We should do some
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more experiments on different x86 machines.
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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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How to decide when to use the "floating point version" of logical ops? Here are
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some code fragments:
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movaps LCPI5_5, %xmm2
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divps %xmm1, %xmm2
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mulps %xmm2, %xmm3
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mulps 8656(%ecx), %xmm3
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addps 8672(%ecx), %xmm3
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andps LCPI5_6, %xmm2
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andps LCPI5_1, %xmm3
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por %xmm2, %xmm3
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movdqa %xmm3, (%edi)
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movaps LCPI5_5, %xmm1
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divps %xmm0, %xmm1
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mulps %xmm1, %xmm3
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mulps 8656(%ecx), %xmm3
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addps 8672(%ecx), %xmm3
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andps LCPI5_6, %xmm1
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andps LCPI5_1, %xmm3
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orps %xmm1, %xmm3
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movaps %xmm3, 112(%esp)
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movaps %xmm3, (%ebx)
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Due to some minor source change, the later case ended up using orps and movaps
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instead of por and movdqa. Does it matter?
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//===---------------------------------------------------------------------===//
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X86RegisterInfo::copyRegToReg() returns X86::MOVAPSrr for VR128. Is it possible
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to choose between movaps, movapd, and movdqa based on types of source and
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destination?
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How about andps, andpd, and pand? Do we really care about the type of the packed
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elements? If not, why not always use the "ps" variants which are likely to be
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shorter.
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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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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25500
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LLVM is producing bad code.
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LBB_main_4: # cond_true44
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addps %xmm1, %xmm2
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subps %xmm3, %xmm2
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movaps (%ecx), %xmm4
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movaps %xmm2, %xmm1
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addps %xmm4, %xmm1
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addl $16, %ecx
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incl %edx
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cmpl $262144, %edx
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movaps %xmm3, %xmm2
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movaps %xmm4, %xmm3
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jne LBB_main_4 # cond_true44
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There are two problems. 1) No need to two loop induction variables. We can
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compare against 262144 * 16. 2) Known register coalescer issue. We should
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be able eliminate one of the movaps:
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addps %xmm2, %xmm1 <=== Commute!
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subps %xmm3, %xmm1
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movaps (%ecx), %xmm4
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movaps %xmm1, %xmm1 <=== Eliminate!
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addps %xmm4, %xmm1
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addl $16, %ecx
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incl %edx
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cmpl $262144, %edx
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movaps %xmm3, %xmm2
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movaps %xmm4, %xmm3
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jne LBB_main_4 # cond_true44
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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 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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__m128d test1( __m128d A, __m128d B) {
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return _mm_shuffle_pd(A, B, 0x3);
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}
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compiles to
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shufpd $3, %xmm1, %xmm0
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Perhaps it's better to use unpckhpd instead?
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unpckhpd %xmm1, %xmm0
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Don't know if unpckhpd is faster. But it is shorter.
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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
|
|
movaps %xmm1, _a
|
|
ret
|
|
|
|
"y" looks good, but "x" does silly movzwl stuff around into a GPR. It seems
|
|
like movd would be sufficient in both cases as the value is already zero
|
|
extended in the 32-bit stack slot IIRC. For signed short, it should also be
|
|
save, as a really-signed value would be undefined for pslld.
|
|
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
#include <math.h>
|
|
int t1(double d) { return signbit(d); }
|
|
|
|
This currently compiles to:
|
|
subl $12, %esp
|
|
movsd 16(%esp), %xmm0
|
|
movsd %xmm0, (%esp)
|
|
movl 4(%esp), %eax
|
|
shrl $31, %eax
|
|
addl $12, %esp
|
|
ret
|
|
|
|
We should use movmskp{s|d} instead.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
CodeGen/X86/vec_align.ll tests whether we can turn 4 scalar loads into a single
|
|
(aligned) vector load. This functionality has a couple of problems.
|
|
|
|
1. The code to infer alignment from loads of globals is in the X86 backend,
|
|
not the dag combiner. This is because dagcombine2 needs to be able to see
|
|
through the X86ISD::Wrapper node, which DAGCombine can't really do.
|
|
2. The code for turning 4 x load into a single vector load is target
|
|
independent and should be moved to the dag combiner.
|
|
3. The code for turning 4 x load into a vector load can only handle a direct
|
|
load from a global or a direct load from the stack. It should be generalized
|
|
to handle any load from P, P+4, P+8, P+12, where P can be anything.
|
|
4. The alignment inference code cannot handle loads from globals in non-static
|
|
mode because it doesn't look through the extra dyld stub load. If you try
|
|
vec_align.ll without -relocation-model=static, you'll see what I mean.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We should lower store(fneg(load p), q) into an integer load+xor+store, which
|
|
eliminates a constant pool load. For example, consider:
|
|
|
|
define i64 @ccosf(float %z.0, float %z.1) nounwind readonly {
|
|
entry:
|
|
%tmp6 = sub float -0.000000e+00, %z.1 ; <float> [#uses=1]
|
|
%tmp20 = tail call i64 @ccoshf( float %tmp6, float %z.0 ) nounwind readonly
|
|
ret i64 %tmp20
|
|
}
|
|
|
|
This currently compiles to:
|
|
|
|
LCPI1_0: # <4 x float>
|
|
.long 2147483648 # float -0
|
|
.long 2147483648 # float -0
|
|
.long 2147483648 # float -0
|
|
.long 2147483648 # float -0
|
|
_ccosf:
|
|
subl $12, %esp
|
|
movss 16(%esp), %xmm0
|
|
movss %xmm0, 4(%esp)
|
|
movss 20(%esp), %xmm0
|
|
xorps LCPI1_0, %xmm0
|
|
movss %xmm0, (%esp)
|
|
call L_ccoshf$stub
|
|
addl $12, %esp
|
|
ret
|
|
|
|
Note the load into xmm0, then xor (to negate), then store. In PIC mode,
|
|
this code computes the pic base and does two loads to do the constant pool
|
|
load, so the improvement is much bigger.
|
|
|
|
The tricky part about this xform is that the argument load/store isn't exposed
|
|
until post-legalize, and at that point, the fneg has been custom expanded into
|
|
an X86 fxor. This means that we need to handle this case in the x86 backend
|
|
instead of in target independent code.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
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://6037315
|
|
|
|
llvm-gcc-4.2 does the following for uint32_t -> float conversions on i386:
|
|
|
|
uint32_t x;
|
|
float y = (float)x;
|
|
|
|
becomes:
|
|
|
|
movl %eax, -8(%ebp) // write x to the stack
|
|
movl $0x3ff00000, -4(%ebp) // 2^52 + x as a double at -4(%ebp)
|
|
movsd -8(%ebp), %xmm0
|
|
subsd [2^52 double], %xmm0 // subtract 2^52 -- this is exact
|
|
cvtsd2ss %xmm0, %xmm0 // convert to single -- rounding happens here
|
|
|
|
On merom/yonah, this takes a substantial stall. The following is a much
|
|
better option:
|
|
|
|
movd %eax, %xmm0 // load x into low word of xmm0
|
|
movsd [2^52 double], %xmm1 // load 2^52 into xmm1
|
|
orpd %xmm1, %xmm0 // 2^52 + x in double precision
|
|
subsd %xmm1, %xmm0 // x in double precision
|
|
cvtsd2ss %xmm0, %xmm0 // x rounded to single precision
|
|
|
|
IF we don't already need PIC, then the following is even faster still, at a
|
|
small cost to code size:
|
|
|
|
movl $0x3ff00000, %ecx // conjure high word of 2^52
|
|
movd %ecx, %xmm1
|
|
movss %eax, %xmm0 // load x into low word of xmm0
|
|
psllq $32, %xmm1 // 2^52
|
|
orpd %xmm1, %xmm0 // 2^52 + x in double precision
|
|
subsd %xmm1, %xmm0 // x in double precision
|
|
cvtsd2ss %xmm0, %xmm0 // x in single precision
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
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.
|
|
|