[PATCH] D79422: [ValueTracking] fix CannotBeNegativeZero() to disregard 'nsz' FMF

[Sanjay Patel via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGa954b8a363ad: [ValueTracking] fix CannotBeNegativeZero() to disregard 'nsz' FMF (authored by spatel).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D79422/new/

https://reviews.llvm.org/D79422

Files:
  llvm/docs/LangRef.rst
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/InstSimplify/fast-math.ll


Index: llvm/test/Transforms/InstSimplify/fast-math.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/fast-math.ll
+++ llvm/test/Transforms/InstSimplify/fast-math.ll
@@ -293,10 +293,13 @@
   ret float %add
 }
 
+; 'nsz' does not guarantee that -0.0 does not occur, so this does not simplify.
+
 define float @fold_fadd_cannot_be_neg0_nsz_src_x_0(float %a, float %b) {
 ; CHECK-LABEL: @fold_fadd_cannot_be_neg0_nsz_src_x_0(
 ; CHECK-NEXT:    [[NSZ:%.*]] = fmul nsz float [[A:%.*]], [[B:%.*]]
-; CHECK-NEXT:    ret float [[NSZ]]
+; CHECK-NEXT:    [[ADD:%.*]] = fadd float [[NSZ]], 0.000000e+00
+; CHECK-NEXT:    ret float [[ADD]]
 ;
   %nsz = fmul nsz float %a, %b
   %add = fadd float %nsz, 0.0
@@ -313,11 +316,14 @@
   ret float %add
 }
 
+; 'nsz' does not guarantee that -0.0 does not occur, so this does not simplify.
+
 define float @fold_fadd_cannot_be_neg0_sqrt_nsz_src_x_0(float %a, float %b) {
 ; CHECK-LABEL: @fold_fadd_cannot_be_neg0_sqrt_nsz_src_x_0(
 ; CHECK-NEXT:    [[NSZ:%.*]] = fmul nsz float [[A:%.*]], [[B:%.*]]
 ; CHECK-NEXT:    [[SQRT:%.*]] = call float @llvm.sqrt.f32(float [[NSZ]])
-; CHECK-NEXT:    ret float [[SQRT]]
+; CHECK-NEXT:    [[ADD:%.*]] = fadd float [[SQRT]], 0.000000e+00
+; CHECK-NEXT:    ret float [[ADD]]
 ;
   %nsz = fmul nsz float %a, %b
   %sqrt = call float @llvm.sqrt.f32(float %nsz)
@@ -325,11 +331,14 @@
   ret float %add
 }
 
+; 'nsz' does not guarantee that -0.0 does not occur, so this does not simplify.
+
 define float @fold_fadd_cannot_be_neg0_canonicalize_nsz_src_x_0(float %a, float %b) {
 ; CHECK-LABEL: @fold_fadd_cannot_be_neg0_canonicalize_nsz_src_x_0(
 ; CHECK-NEXT:    [[NSZ:%.*]] = fmul nsz float [[A:%.*]], [[B:%.*]]
 ; CHECK-NEXT:    [[CANON:%.*]] = call float @llvm.canonicalize.f32(float [[NSZ]])
-; CHECK-NEXT:    ret float [[CANON]]
+; CHECK-NEXT:    [[ADD:%.*]] = fadd float [[CANON]], 0.000000e+00
+; CHECK-NEXT:    ret float [[ADD]]
 ;
   %nsz = fmul nsz float %a, %b
   %canon = call float @llvm.canonicalize.f32(float %nsz)
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -3202,6 +3202,9 @@
 
 /// Return true if we can prove that the specified FP value is never equal to
 /// -0.0.
+/// NOTE: Do not check 'nsz' here because that fast-math-flag does not guarantee
+///       that a value is not -0.0. It only guarantees that -0.0 may be treated
+///       the same as +0.0 in floating-point ops.
 ///
 /// NOTE: this function will need to be revisited when we support non-default
 /// rounding modes!
@@ -3218,11 +3221,6 @@
   if (!Op)
     return false;
 
-  // Check if the nsz fast-math flag is set.
-  if (auto *FPO = dyn_cast<FPMathOperator>(Op))
-    if (FPO->hasNoSignedZeros())
-      return true;
-
   // (fadd x, 0.0) is guaranteed to return +0.0, not -0.0.
   if (match(Op, m_FAdd(m_Value(), m_PosZeroFP())))
     return true;
Index: llvm/docs/LangRef.rst
===================================================================
--- llvm/docs/LangRef.rst
+++ llvm/docs/LangRef.rst
@@ -2727,7 +2727,8 @@
 
 ``nsz``
    No Signed Zeros - Allow optimizations to treat the sign of a zero
-   argument or result as insignificant.
+   argument or result as insignificant. This does not imply that -0.0
+   is poison and/or guaranteed to not exist in the operation.
 
 ``arcp``
    Allow Reciprocal - Allow optimizations to use the reciprocal of an


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