[llvm] r362879 - [InstSimplify] enhance fcmp fold with never-nan operand

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Sat Jun  8 08:12:33 2019
New Revision: 362879

URL: http://llvm.org/viewvc/llvm-project?rev=362879&view=rev
Log:
[InstSimplify] enhance fcmp fold with never-nan operand

This is 1 step towards correcting our usage of fast-math-flags when applied on an fcmp.
In this case, we are checking for 'nnan' on the fcmp itself rather than the operand of
the fcmp. But I'm leaving that clause in until we're more confident that we can stop
relying on fcmp's FMF.

By using the more general "isKnownNeverNaN()", we gain a simplification shown on the
tests with 'uitofp' regardless of the FMF on the fcmp (uitofp never produces a NaN).
On the tests with 'fabs', we are now relying on the FMF for the call fabs instruction
in addition to the FMF on the fcmp.

I'll update the 'ult' case below here as a follow-up assuming no problems here.

Differential Revision: https://reviews.llvm.org/D62979

Modified:
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp
    llvm/trunk/test/Transforms/InstSimplify/floating-point-compare.ll

Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=362879&r1=362878&r2=362879&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Sat Jun  8 08:12:33 2019
@@ -3477,7 +3477,8 @@ static Value *SimplifyFCmpInst(unsigned
   if (match(RHS, m_AnyZeroFP())) {
     switch (Pred) {
     case FCmpInst::FCMP_OGE:
-      if (FMF.noNaNs() && CannotBeOrderedLessThanZero(LHS, Q.TLI))
+      if ((FMF.noNaNs() || isKnownNeverNaN(LHS, Q.TLI)) &&
+          CannotBeOrderedLessThanZero(LHS, Q.TLI))
         return getTrue(RetTy);
       break;
     case FCmpInst::FCMP_UGE:
@@ -3485,6 +3486,7 @@ static Value *SimplifyFCmpInst(unsigned
         return getTrue(RetTy);
       break;
     case FCmpInst::FCMP_ULT:
+      // TODO: This should match 'oge'.
       if (FMF.noNaNs() && CannotBeOrderedLessThanZero(LHS, Q.TLI))
         return getFalse(RetTy);
       break;

Modified: llvm/trunk/test/Transforms/InstSimplify/floating-point-compare.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/floating-point-compare.ll?rev=362879&r1=362878&r2=362879&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/floating-point-compare.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/floating-point-compare.ll Sat Jun  8 08:12:33 2019
@@ -257,9 +257,7 @@ define <2 x i1> @UIToFP_is_nan_or_positi
 
 define i1 @UIToFP_is_positive_or_zero(i32 %x) {
 ; CHECK-LABEL: @UIToFP_is_positive_or_zero(
-; CHECK-NEXT:    [[A:%.*]] = uitofp i32 [[X:%.*]] to float
-; CHECK-NEXT:    [[R:%.*]] = fcmp oge float [[A]], 0.000000e+00
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 true
 ;
   %a = uitofp i32 %x to float
   %r = fcmp oge float %a, 0.000000e+00
@@ -268,9 +266,7 @@ define i1 @UIToFP_is_positive_or_zero(i3
 
 define <2 x i1> @UIToFP_is_positive_or_zero_vec(<2 x i32> %x) {
 ; CHECK-LABEL: @UIToFP_is_positive_or_zero_vec(
-; CHECK-NEXT:    [[A:%.*]] = uitofp <2 x i32> [[X:%.*]] to <2 x float>
-; CHECK-NEXT:    [[R:%.*]] = fcmp oge <2 x float> [[A]], zeroinitializer
-; CHECK-NEXT:    ret <2 x i1> [[R]]
+; CHECK-NEXT:    ret <2 x i1> <i1 true, i1 true>
 ;
   %a = uitofp <2 x i32> %x to <2 x float>
   %r = fcmp oge <2 x float> %a, zeroinitializer
@@ -351,9 +347,7 @@ define <2 x i1> @fabs_is_nan_or_positive
 
 define i1 @fabs_nnan_is_positive_or_zero(double %x) {
 ; CHECK-LABEL: @fabs_nnan_is_positive_or_zero(
-; CHECK-NEXT:    [[FABS:%.*]] = tail call nnan double @llvm.fabs.f64(double [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = fcmp oge double [[FABS]], 0.000000e+00
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %fabs = tail call nnan double @llvm.fabs.f64(double %x)
   %cmp = fcmp oge double %fabs, 0.0
@@ -362,9 +356,7 @@ define i1 @fabs_nnan_is_positive_or_zero
 
 define <2 x i1> @fabs_nnan_is_positive_or_zero_vec(<2 x double> %x) {
 ; CHECK-LABEL: @fabs_nnan_is_positive_or_zero_vec(
-; CHECK-NEXT:    [[FABS:%.*]] = tail call nnan <2 x double> @llvm.fabs.v2f64(<2 x double> [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = fcmp oge <2 x double> [[FABS]], zeroinitializer
-; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+; CHECK-NEXT:    ret <2 x i1> <i1 true, i1 true>
 ;
   %fabs = tail call nnan <2 x double> @llvm.fabs.v2f64(<2 x double> %x)
   %cmp = fcmp oge <2 x double> %fabs, zeroinitializer