Merging r338716:

------------------------------------------------------------------------
r338716 | spatel | 2018-08-02 15:46:20 +0200 (Thu, 02 Aug 2018) | 41 lines

[ValueTracking] fix maxnum miscompile for cannotBeOrderedLessThanZero (PR37776)

This adds the NAN checks suggested in PR37776:
https://bugs.llvm.org/show_bug.cgi?id=37776

If both operands to maxnum are NAN, that should get constant folded, so we don't
have to handle that case. This is the same assumption as other FP ops in this
function. Returning 'false' is always conservatively correct.

Copying from the bug report:

Currently, we have this for "when is cannotBeOrderedLessThanZero
(mustBePositiveOrNaN) true for maxnum":
               L
        -------------------
        | Pos | Neg | NaN |
   ------------------------
   |Pos |  x  |  x  |  x  |
   ------------------------
 R |Neg |  x  |     |  x  |
   ------------------------
   |NaN |  x  |  x  |  x  |
   ------------------------

The cases with (Neg & NaN) are wrong. We should have:

                L
        -------------------
        | Pos | Neg | NaN |
   ------------------------
   |Pos |  x  |  x  |  x  |
   ------------------------
 R |Neg |  x  |     |     |
   ------------------------
   |NaN |  x  |     |  x  |
   ------------------------

Differential Revision: https://reviews.llvm.org/D50081

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_70@339234 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 0ef3916..edd46c5 100644 (file)
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -2817,10 +2817,13 @@ static bool cannotBeOrderedLessThanZeroImpl(const Value *V,
     default:
       break;
     case Intrinsic::maxnum:
-      return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly,
-                                             Depth + 1) ||
-             cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly,
-                                             Depth + 1);
+      return (isKnownNeverNaN(I->getOperand(0)) &&
+              cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI,
+                                              SignBitOnly, Depth + 1)) ||
+             (isKnownNeverNaN(I->getOperand(1)) &&
+              cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI,
+                                              SignBitOnly, Depth + 1));
+
     case Intrinsic::minnum:
       return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly,
                                              Depth + 1) &&

diff --git a/test/Transforms/InstSimplify/floating-point-compare.ll b/test/Transforms/InstSimplify/floating-point-compare.ll
index b1444bb..bc5c58a 100644 (file)
--- a/test/Transforms/InstSimplify/floating-point-compare.ll
+++ b/test/Transforms/InstSimplify/floating-point-compare.ll
@@ -266,13 +266,15 @@ define i1 @orderedLessZeroMinNum(float, float) {
   ret i1 %uge
 }
 
-; FIXME: This is wrong.
 ; PR37776: https://bugs.llvm.org/show_bug.cgi?id=37776
 ; exp() may return nan, leaving %1 as the unknown result, so we can't simplify.
 
 define i1 @orderedLessZeroMaxNum(float, float) {
 ; CHECK-LABEL: @orderedLessZeroMaxNum(
-; CHECK-NEXT:    ret i1 true
+; CHECK-NEXT:    [[A:%.*]] = call float @llvm.exp.f32(float [[TMP0:%.*]])
+; CHECK-NEXT:    [[B:%.*]] = call float @llvm.maxnum.f32(float [[A]], float [[TMP1:%.*]])
+; CHECK-NEXT:    [[UGE:%.*]] = fcmp uge float [[B]], 0.000000e+00
+; CHECK-NEXT:    ret i1 [[UGE]]
 ;
   %a = call float @llvm.exp.f32(float %0)
   %b = call float @llvm.maxnum.f32(float %a, float %1)