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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Matt Arsenault (arsenm)

<details>
<summary>Changes</summary>

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.

---
Full diff: https://github.com/llvm/llvm-project/pull/178157.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp (+5-3) 
- (modified) llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll (+1-1) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 61e93e0398be7..ff56982c4ff5e 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 b76b945e92adc..c832aeb1ac0ef 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
@@ -1294,7 +1294,7 @@ 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]])

``````````

</details>


https://github.com/llvm/llvm-project/pull/178157