[llvm] ff79d7d - InstCombine: Apply demanded mask at recursion limit in SimplifyDemandedFPClass (#178157)

[via llvm-commits]

Author: Matt Arsenault
Date: 2026-01-27T18:19:55+01:00
New Revision: ff79d7d1bf0415e52ad542b059c55f0e92b3bad6

URL: https://github.com/llvm/llvm-project/commit/ff79d7d1bf0415e52ad542b059c55f0e92b3bad6
DIFF: https://github.com/llvm/llvm-project/commit/ff79d7d1bf0415e52ad542b059c55f0e92b3bad6.diff

LOG: InstCombine: Apply demanded mask at recursion limit in SimplifyDemandedFPClass (#178157)

This fixes missed flag inference in some cases, due to not inferring
no-nan result implies no-nan source. Also start treating explicit
nofpclass
attributes as a leaf value, like a constant or argument.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
    llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index d9e9c25b4fb45..25df44e94699d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -3423,14 +3423,16 @@ bool InstCombinerImpl::SimplifyDemandedFPClass(Instruction *I, unsigned OpNo,
     return true;
   }
 
-  if (Depth == MaxAnalysisRecursionDepth)
-    return false;
-
   if (const CallBase *CB = dyn_cast<CallBase>(VInst)) {
     FPClassTest NoFPClass = CB->getParamNoFPClass(U.getOperandNo());
     DemandedMask &= ~NoFPClass;
   }
 
+  if (Depth == MaxAnalysisRecursionDepth) {
+    Known.knownNot(~DemandedMask);
+    return false;
+  }
+
   Value *NewVal;
 
   if (VInst->hasOneUse()) {

diff  --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
index 48a7514c07d66..e10c920a9ae9a 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
@@ -1311,7 +1311,7 @@ define nofpclass(nan inf) float @pow_f32(float nofpclass(nan inf) %arg, float no
 ; CHECK-SAME: (float nofpclass(nan inf) [[ARG:%.*]], float nofpclass(nan inf) [[ARG1:%.*]]) {
 ; CHECK-NEXT:  bb:
 ; CHECK-NEXT:    [[I:%.*]] = tail call nofpclass(ninf nzero nsub nnorm) float @llvm.fabs.f32(float noundef [[ARG]])
-; CHECK-NEXT:    [[I2:%.*]] = tail call float @llvm.log2.f32(float noundef [[I]])
+; CHECK-NEXT:    [[I2:%.*]] = tail call nnan float @llvm.log2.f32(float [[I]])
 ; CHECK-NEXT:    [[I3:%.*]] = fmul nnan float [[I2]], [[ARG1]]
 ; CHECK-NEXT:    [[I4:%.*]] = tail call nnan float @llvm.exp2.f32(float [[I3]])
 ; CHECK-NEXT:    [[I5:%.*]] = tail call nofpclass(ninf nzero nsub nnorm) float @llvm.fabs.f32(float noundef [[ARG1]])