Utilize new SDNode flag functionality to expand current support for fadd

Summary: This patch originated from D46562 and is a proper subset, with some issues addressed.

Reviewers: spatel, hfinkel, wristow, arsenm, javed.absar

Reviewed By: spatel

Subscribers: wdng, nhaehnle

Differential Revision: https://reviews.llvm.org/D47909

llvm-svn: 334996

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -10327,20 +10327,21 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
     return DAG.getNode(ISD::FSUB, DL, VT, N1IsFMul ? N0 : N1, Add, Flags);
   }
 
-  // FIXME: Auto-upgrade the target/function-level option.
-  if (Options.NoSignedZerosFPMath || N->getFlags().hasNoSignedZeros()) {
-    // fold (fadd A, 0) -> A
-    if (ConstantFPSDNode *N1C = isConstOrConstSplatFP(N1))
-      if (N1C->isZero())
-        return N0;
+  ConstantFPSDNode *N1C = isConstOrConstSplatFP(N1);
+  if (N1C && N1C->isZero()) {
+    if (N1C->isNegative() || Options.UnsafeFPMath ||
+        Flags.hasNoSignedZeros()) {
+      // fold (fadd A, 0) -> A
+      return N0;
+    }
   }
 
   // No FP constant should be created after legalization as Instruction
   // Selection pass has a hard time dealing with FP constants.
   bool AllowNewConst = (Level < AfterLegalizeDAG);
 
-  // TODO: fmf test for NaNs could be done here too
-  if (Options.UnsafeFPMath && AllowNewConst) {
+  // If 'unsafe math' or nnan is enabled, fold lots of things.
+  if ((Options.UnsafeFPMath || Flags.hasNoNaNs()) && AllowNewConst) {
     // If allowed, fold (fadd (fneg x), x) -> 0.0
     if (N0.getOpcode() == ISD::FNEG && N0.getOperand(0) == N1)
       return DAG.getConstantFP(0.0, DL, VT);
@@ -10350,9 +10351,12 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
       return DAG.getConstantFP(0.0, DL, VT);
   }
 
-  // If 'unsafe math' is enabled, fold lots of things.
-  // TODO: fmf testing for reassoc/nsz could be done here too
-  if (Options.UnsafeFPMath && AllowNewConst) {
+  // If 'unsafe math' or reassoc and nsz, fold lots of things.
+  // TODO: break out portions of the transformations below for which Unsafe is
+  //       considered and which do not require both nsz and reassoc
+  if ((Options.UnsafeFPMath ||
+       (Flags.hasAllowReassociation() && Flags.hasNoSignedZeros())) &&
+      AllowNewConst) {
     // fadd (fadd x, c1), c2 -> fadd x, c1 + c2
     if (N1CFP && N0.getOpcode() == ISD::FADD &&
         isConstantFPBuildVectorOrConstantFP(N0.getOperand(1))) {

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -4442,24 +4442,6 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
   case ISD::FMUL:
   case ISD::FDIV:
   case ISD::FREM:
-    if (getTarget().Options.UnsafeFPMath) {
-      if (Opcode == ISD::FADD) {
-        // x+0 --> x
-        if (N2CFP && N2CFP->getValueAPF().isZero())
-          return N1;
-      } else if (Opcode == ISD::FSUB) {
-        // x-0 --> x
-        if (N2CFP && N2CFP->getValueAPF().isZero())
-          return N1;
-      } else if (Opcode == ISD::FMUL) {
-        // x*0 --> 0
-        if (N2CFP && N2CFP->isZero())
-          return N2;
-        // x*1 --> x
-        if (N2CFP && N2CFP->isExactlyValue(1.0))
-          return N1;
-      }
-    }
     assert(VT.isFloatingPoint() && "This operator only applies to FP types!");
     assert(N1.getValueType() == N2.getValueType() &&
            N1.getValueType() == VT && "Binary operator types must match!");

llvm/test/CodeGen/AArch64/fadd-combines.ll

@@ -100,11 +100,12 @@ define float @fadd_const_multiuse_fmf(float %x) {
 ; CHECK-LABEL: fadd_const_multiuse_fmf:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    adrp x8, .LCPI7_0
+; CHECK-NEXT:    adrp x9, .LCPI7_1
 ; CHECK-NEXT:    ldr s1, [x8, :lo12:.LCPI7_0]
-; CHECK-NEXT:    fadd s0, s0, s1
-; CHECK-NEXT:    fmov s1, #17.00000000
+; CHECK-NEXT:    ldr s2, [x9, :lo12:.LCPI7_1]
 ; CHECK-NEXT:    fadd s1, s0, s1
-; CHECK-NEXT:    fadd s0, s0, s1
+; CHECK-NEXT:    fadd s0, s0, s2
+; CHECK-NEXT:    fadd s0, s1, s0
 ; CHECK-NEXT:    ret
   %a1 = fadd float %x, 42.0
   %a2 = fadd nsz reassoc float %a1, 17.0

llvm/test/CodeGen/AMDGPU/fadd.ll

@@ -66,7 +66,7 @@ define amdgpu_kernel void @fadd_v8f32(<8 x float> addrspace(1)* %out, <8 x float
 ; FUNC-LABEL: {{^}}fadd_0_nsz_attr_f32:
 ; SI-NOT: v_add_f32
 define amdgpu_kernel void @fadd_0_nsz_attr_f32(float addrspace(1)* %out, float %a) #1 {
-   %add = fadd float %a, 0.0
+   %add = fadd nsz float %a, 0.0
    store float %add, float addrspace(1)* %out, align 4
    ret void
 }

llvm/test/CodeGen/X86/fmf-flags.ll

@@ -32,18 +32,13 @@ declare float @llvm.fmuladd.f32(float %a, float %b, float %c);
 define float @fast_fmuladd_opts(float %a , float %b , float %c) {
 ; X64-LABEL: fast_fmuladd_opts:
 ; X64:       # %bb.0:
-; X64-NEXT:    movaps %xmm0, %xmm1
-; X64-NEXT:    addss %xmm0, %xmm1
-; X64-NEXT:    addss %xmm0, %xmm1
-; X64-NEXT:    movaps %xmm1, %xmm0
+; X64-NEXT:    mulss {{.*}}(%rip), %xmm0
 ; X64-NEXT:    retq
 ;
 ; X86-LABEL: fast_fmuladd_opts:
 ; X86:       # %bb.0:
 ; X86-NEXT:    flds {{[0-9]+}}(%esp)
-; X86-NEXT:    fld %st(0)
-; X86-NEXT:    fadd %st(1)
-; X86-NEXT:    faddp %st(1)
+; X86-NEXT:    fmuls {{.*}}
 ; X86-NEXT:    retl
   %res = call fast float @llvm.fmuladd.f32(float %a, float 2.0, float %a)
   ret float %res
@@ -56,9 +51,9 @@ define float @fast_fmuladd_opts(float %a , float %b , float %c) {
 define double @not_so_fast_mul_add(double %x) {
 ; X64-LABEL: not_so_fast_mul_add:
 ; X64:       # %bb.0:
-; X64-NEXT:    movsd {{.*#+}} xmm1 = mem[0],zero
+; X64-NEXT:    movsd {{.*}}(%rip), %xmm1
 ; X64-NEXT:    mulsd %xmm0, %xmm1
-; X64-NEXT:    addsd %xmm1, %xmm0
+; X64-NEXT:    mulsd {{.*}}(%rip), %xmm0
 ; X64-NEXT:    movsd %xmm1, {{.*}}(%rip)
 ; X64-NEXT:    retq
 ;
@@ -67,7 +62,9 @@ define double @not_so_fast_mul_add(double %x) {
 ; X86-NEXT:    fldl {{[0-9]+}}(%esp)
 ; X86-NEXT:    fld %st(0)
 ; X86-NEXT:    fmull {{\.LCPI.*}}
-; X86-NEXT:    fadd %st(0), %st(1)
+; X86-NEXT:    fxch %st(1)
+; X86-NEXT:    fmull {{\.LCPI.*}}
+; X86-NEXT:    fxch %st(1)
 ; X86-NEXT:    fstpl mul1
 ; X86-NEXT:    retl
   %m = fmul double %x, 4.2

llvm/test/CodeGen/X86/fp-fold.ll

@@ -17,18 +17,33 @@ define float @fadd_zero(float %x) {
 }
 
 define float @fadd_negzero(float %x) {
-; STRICT-LABEL: fadd_negzero:
-; STRICT:       # %bb.0:
-; STRICT-NEXT:    addss {{.*}}(%rip), %xmm0
-; STRICT-NEXT:    retq
-;
-; UNSAFE-LABEL: fadd_negzero:
-; UNSAFE:       # %bb.0:
-; UNSAFE-NEXT:    retq
+; ANY-LABEL: fadd_negzero:
+; ANY:       # %bb.0:
+; ANY-NEXT:    retq
   %r = fadd float %x, -0.0
   ret float %r
 }
 
+define float @fadd_produce_zero(float %x) {
+; ANY-LABEL: fadd_produce_zero:
+; ANY:       # %bb.0:
+; ANY-NEXT:    xorps %xmm0, %xmm0
+; ANY-NEXT:    retq
+  %neg = fsub nsz float 0.0, %x
+  %r = fadd nnan float %neg, %x
+  ret float %r
+}
+
+define float @fadd_reassociate(float %x) {
+; ANY-LABEL: fadd_reassociate:
+; ANY:       # %bb.0:
+; ANY-NEXT:    addss {{.*}}(%rip), %xmm0
+; ANY-NEXT:    retq
+  %sum = fadd float %x, 8.0
+  %r = fadd reassoc nsz float %sum, 12.0
+  ret float %r
+}
+
 define float @fadd_negzero_nsz(float %x) {
 ; ANY-LABEL: fadd_negzero_nsz:
 ; ANY:       # %bb.0: