[llvm] [InstCombine] Preserve the flag from RHS only if the `and` is bitwise (PR #113164)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: XChy (XChy)

<details>
<summary>Changes</summary>

Fixes #<!-- -->113123
Alive proof: https://alive2.llvm.org/ce/z/hnqeLC

---
Full diff: https://github.com/llvm/llvm-project/pull/113164.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (+4-2) 
- (modified) llvm/test/Transforms/InstCombine/fcmp-range-check-idiom.ll (+39) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index ed9a89b14efcca..678149f56eb901 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1444,8 +1444,10 @@ Value *InstCombinerImpl::foldLogicOfFCmps(FCmpInst *LHS, FCmpInst *RHS,
     }
     if (IsLessThanOrLessEqual(IsAnd ? PredL : PredR)) {
       BuilderTy::FastMathFlagGuard Guard(Builder);
-      Builder.setFastMathFlags(LHS->getFastMathFlags() |
-                               RHS->getFastMathFlags());
+      FastMathFlags NewFlag = LHS->getFastMathFlags();
+      if (!IsLogicalSelect)
+        NewFlag |= RHS->getFastMathFlags();
+      Builder.setFastMathFlags(NewFlag);
 
       Value *FAbs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, LHS0);
       return Builder.CreateFCmp(PredL, FAbs,
diff --git a/llvm/test/Transforms/InstCombine/fcmp-range-check-idiom.ll b/llvm/test/Transforms/InstCombine/fcmp-range-check-idiom.ll
index 10a3ccf3cdb48a..54dbb09cb8fd31 100644
--- a/llvm/test/Transforms/InstCombine/fcmp-range-check-idiom.ll
+++ b/llvm/test/Transforms/InstCombine/fcmp-range-check-idiom.ll
@@ -359,3 +359,42 @@ define i1 @test_and_olt_fmf_propagation_union(float %x) {
   %cond = and i1 %cmp1, %cmp2
   ret i1 %cond
 }
+
+define i1 @test_and_olt_fmf_propagation_union_logical_rhs_poison(float %x) {
+; CHECK-LABEL: define i1 @test_and_olt_fmf_propagation_union_logical_rhs_poison(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    [[COND:%.*]] = fcmp olt float [[TMP1]], 0x3C00000000000000
+; CHECK-NEXT:    ret i1 [[COND]]
+;
+  %cmp1 = fcmp ninf olt float %x, 0x3C00000000000000
+  %cmp2 = fcmp ogt float %x, 0xBC00000000000000
+  %cond = select i1 %cmp2, i1 %cmp1, i1 false
+  ret i1 %cond
+}
+
+define i1 @test_and_olt_fmf_propagation_union_logical_lhs_poison(float %x) {
+; CHECK-LABEL: define i1 @test_and_olt_fmf_propagation_union_logical_lhs_poison(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = call ninf float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    [[COND:%.*]] = fcmp ninf olt float [[TMP1]], 0x3C00000000000000
+; CHECK-NEXT:    ret i1 [[COND]]
+;
+  %cmp1 = fcmp olt float %x, 0x3C00000000000000
+  %cmp2 = fcmp ninf ogt float %x, 0xBC00000000000000
+  %cond = select i1 %cmp2, i1 %cmp1, i1 false
+  ret i1 %cond
+}
+
+define i1 @test_and_olt_fmf_propagation_union_logical_both_poison(float %x) {
+; CHECK-LABEL: define i1 @test_and_olt_fmf_propagation_union_logical_both_poison(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = call ninf float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    [[COND:%.*]] = fcmp ninf olt float [[TMP1]], 0x3C00000000000000
+; CHECK-NEXT:    ret i1 [[COND]]
+;
+  %cmp1 = fcmp ninf olt float %x, 0x3C00000000000000
+  %cmp2 = fcmp ninf ogt float %x, 0xBC00000000000000
+  %cond = select i1 %cmp2, i1 %cmp1, i1 false
+  ret i1 %cond
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/113164