[llvm] d05c07d - InstCombine: Compute fp class when simplifying with multiple uses (#174086)

[via llvm-commits]

Author: Matt Arsenault
Date: 2025-12-31T14:29:40+01:00
New Revision: d05c07d64af734c0e72cf3c95b7bc926824bb4c1

URL: https://github.com/llvm/llvm-project/commit/d05c07d64af734c0e72cf3c95b7bc926824bb4c1
DIFF: https://github.com/llvm/llvm-project/commit/d05c07d64af734c0e72cf3c95b7bc926824bb4c1.diff

LOG: InstCombine: Compute fp class when simplifying with multiple uses (#174086)

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 85672cdfe1377..19b98080d628a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -2053,8 +2053,10 @@ Value *InstCombinerImpl::SimplifyDemandedUseFPClass(Value *V,
     return FoldedToConst == V ? nullptr : FoldedToConst;
   }
 
-  if (!I->hasOneUse())
+  if (!I->hasOneUse()) {
+    Known = computeKnownFPClass(V, DemandedMask, CxtI, Depth + 1);
     return nullptr;
+  }
 
   if (auto *FPOp = dyn_cast<FPMathOperator>(I)) {
     if (FPOp->hasNoNaNs())

diff  --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
index a7ff967d3123b..c28b5967303c8 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
@@ -1137,8 +1137,7 @@ define nofpclass(inf) float @ret_nofpclass_inf__select_assumed_call_result_only_
 ; CHECK-NEXT:    [[FABS:%.*]] = call float @llvm.fabs.f32(float [[MUST_BE_INF]])
 ; CHECK-NEXT:    [[IS_INF:%.*]] = fcmp oeq float [[FABS]], 0x7FF0000000000000
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[IS_INF]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[COND]], float [[MUST_BE_INF]], float [[Y]]
-; CHECK-NEXT:    ret float [[SELECT]]
+; CHECK-NEXT:    ret float [[Y]]
 ;
   %must.be.inf = call float @extern()
   %fabs = call float @llvm.fabs.f32(float %must.be.inf)
@@ -1340,3 +1339,21 @@ define nofpclass(ninf) float @ret_nofpclass_ninf__maxnum_pinf(i1 %cond, float %x
   %max = call float @llvm.maximumnum.f32(float %x, float 0x7FF0000000000000)
   ret float %max
 }
+
+declare nofpclass(inf norm sub zero) float @returns_nan()
+
+; %nan has multiple uses, but we should still know what class is is
+; %allowing this to fold to a single select.
+define nofpclass(nan) float @known_class_multiple_uses(i1 %cond0, i1 %cond1, i1 %cond2, float %unknown0, float %unknown1) {
+; CHECK-LABEL: define nofpclass(nan) float @known_class_multiple_uses
+; CHECK-SAME: (i1 [[COND0:%.*]], i1 [[COND1:%.*]], i1 [[COND2:%.*]], float [[UNKNOWN0:%.*]], float [[UNKNOWN1:%.*]]) {
+; CHECK-NEXT:    [[NAN:%.*]] = call float @returns_nan()
+; CHECK-NEXT:    [[SELECT2:%.*]] = select i1 [[COND2]], float [[UNKNOWN0]], float [[UNKNOWN1]]
+; CHECK-NEXT:    ret float [[SELECT2]]
+;
+  %nan = call float @returns_nan()
+  %select0 = select i1 %cond0, float %unknown0, float %nan
+  %select1 = select i1 %cond1, float %nan, float %unknown1
+  %select2 = select i1 %cond2, float %select0, float %select1
+  ret float %select2
+}