[Constants] add identity constants for fadd/fmul

As the test diffs show, the current users of getBinOpIdentity()
are InstCombine and Reassociate. SLP vectorizer is a candidate
for using this functionality too (D28907).

The InstCombine shuffle improvements are part of the planned
enhancements noted in D48830.

InstCombine actually has several other uses of getBinOpIdentity() 
via SimplifyUsingDistributiveLaws(), but we don't call that for 
any FP ops. Fixing that might be another part of removing the
custom reassociation in InstCombine that is only done for fadd+fmul.

llvm-svn: 336215

4 files changed, 15 insertions, 15 deletions

diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index 9b8670c7f3f..3ea7598c11e 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -2281,7 +2281,12 @@ Constant *ConstantExpr::getBinOpIdentity(unsigned Opcode, Type *Ty) {
   case Instruction::And:
     return Constant::getAllOnesValue(Ty);
 
-  // FIXME: FAdd / FMul?
+  // TODO: If the fadd has 'nsz', should we return +0.0?
+  case Instruction::FAdd:
+    return ConstantFP::getNegativeZero(Ty);
+
+  case Instruction::FMul:
+    return ConstantFP::get(Ty, 1.0);
   }
 }
 
diff --git a/llvm/test/Transforms/InstCombine/shuffle_select.ll b/llvm/test/Transforms/InstCombine/shuffle_select.ll
index 1b568203372..8f3d13840c8 100644
--- a/llvm/test/Transforms/InstCombine/shuffle_select.ll
+++ b/llvm/test/Transforms/InstCombine/shuffle_select.ll
@@ -163,8 +163,7 @@ define <4 x i32> @srem(<4 x i32> %v) {
 
 define <4 x float> @fadd(<4 x float> %v) {
 ; CHECK-LABEL: @fadd(
-; CHECK-NEXT:    [[B:%.*]] = fadd <4 x float> [[V:%.*]], <float 4.100000e+01, float 4.200000e+01, float 4.300000e+01, float 4.400000e+01>
-; CHECK-NEXT:    [[S:%.*]] = shufflevector <4 x float> [[B]], <4 x float> [[V]], <4 x i32> <i32 0, i32 1, i32 6, i32 7>
+; CHECK-NEXT:    [[S:%.*]] = fadd <4 x float> [[V:%.*]], <float 4.100000e+01, float 4.200000e+01, float -0.000000e+00, float -0.000000e+00>
 ; CHECK-NEXT:    ret <4 x float> [[S]]
 ;
   %b = fadd <4 x float> %v, <float 41.0, float 42.0, float 43.0, float 44.0>
@@ -187,8 +186,7 @@ define <4 x double> @fsub(<4 x double> %v) {
 
 define <4 x float> @fmul(<4 x float> %v) {
 ; CHECK-LABEL: @fmul(
-; CHECK-NEXT:    [[B:%.*]] = fmul nnan ninf <4 x float> [[V:%.*]], <float 4.100000e+01, float 4.200000e+01, float 4.300000e+01, float 4.400000e+01>
-; CHECK-NEXT:    [[S:%.*]] = shufflevector <4 x float> [[B]], <4 x float> [[V]], <4 x i32> <i32 0, i32 5, i32 6, i32 7>
+; CHECK-NEXT:    [[S:%.*]] = fmul nnan ninf <4 x float> [[V:%.*]], <float 4.100000e+01, float 1.000000e+00, float 1.000000e+00, float 1.000000e+00>
 ; CHECK-NEXT:    ret <4 x float> [[S]]
 ;
   %b = fmul nnan ninf <4 x float> %v, <float 41.0, float 42.0, float 43.0, float 44.0>
diff --git a/llvm/test/Transforms/Reassociate/binop-identity.ll b/llvm/test/Transforms/Reassociate/binop-identity.ll
index 12a6c7867ec..13333fad599 100644
--- a/llvm/test/Transforms/Reassociate/binop-identity.ll
+++ b/llvm/test/Transforms/Reassociate/binop-identity.ll
@@ -48,7 +48,7 @@ define i8 @xor_0(i8 %x) {
   ret i8 %a2
 }
 
-; FIXME
+; FIXME - the binop identity constant for fadd is -0.0, so this didn't fold.
 
 define float @fadd_0(float %x) {
 ; CHECK-LABEL: @fadd_0(
@@ -60,12 +60,9 @@ define float @fadd_0(float %x) {
   ret float %a2
 }
 
-; FIXME
-
 define float @fmul_1(float %x) {
 ; CHECK-LABEL: @fmul_1(
-; CHECK-NEXT:    [[A2:%.*]] = fmul fast float [[X:%.*]], 1.000000e+00
-; CHECK-NEXT:    ret float [[A2]]
+; CHECK-NEXT:    ret float [[X:%.*]]
 ;
   %a1 = fmul fast float %x, 4.0
   %a2 = fmul fast float %a1, 0.25
diff --git a/llvm/test/Transforms/Reassociate/reassoc-intermediate-fnegs.ll b/llvm/test/Transforms/Reassociate/reassoc-intermediate-fnegs.ll
index 84287c5c178..3bd8396638a 100644
--- a/llvm/test/Transforms/Reassociate/reassoc-intermediate-fnegs.ll
+++ b/llvm/test/Transforms/Reassociate/reassoc-intermediate-fnegs.ll
@@ -1,11 +1,12 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -reassociate -S | FileCheck %s
 
 ; Input is A op (B op C)
 
 define half @faddsubAssoc1(half %a, half %b) {
 ; CHECK-LABEL: @faddsubAssoc1(
-; CHECK-NEXT:    [[T2_NEG:%.*]] = fmul fast half %a, 0xH4500
-; CHECK-NEXT:    [[REASS_MUL:%.*]] = fmul fast half %b, 0xH4500
+; CHECK-NEXT:    [[T2_NEG:%.*]] = fmul fast half [[A:%.*]], 0xH4500
+; CHECK-NEXT:    [[REASS_MUL:%.*]] = fmul fast half [[B:%.*]], 0xH4500
 ; CHECK-NEXT:    [[T51:%.*]] = fsub fast half [[REASS_MUL]], [[T2_NEG]]
 ; CHECK-NEXT:    [[T5:%.*]] = fadd fast half [[REASS_MUL]], [[T2_NEG]]
 ; CHECK-NEXT:    ret half [[T51]]
@@ -22,9 +23,8 @@ define half @faddsubAssoc1(half %a, half %b) {
 
 define half @faddsubAssoc2(half %a, half %b) {
 ; CHECK-LABEL: @faddsubAssoc2(
-; CHECK-NEXT:    [[T2:%.*]] = fmul fast half %a, 0xH4500
-; CHECK-NEXT:    [[REASS_MUL:%.*]] = fmul fast half %b, 0xH3C00
-; CHECK-NEXT:    [[T5:%.*]] = fadd fast half [[REASS_MUL]], [[T2]]
+; CHECK-NEXT:    [[T2:%.*]] = fmul fast half [[A:%.*]], 0xH4500
+; CHECK-NEXT:    [[T5:%.*]] = fadd fast half [[B:%.*]], [[T2]]
 ; CHECK-NEXT:    ret half [[T5]]
 ;
   %t1 = fmul fast half %b, 0xH4200 ; 3*b