[llvm] [InstCombine] Fix FMF propagation in `foldFCmpFSubIntoFCmp` (PR #161539)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

Proof: https://alive2.llvm.org/ce/z/orSP-S
Closes https://github.com/llvm/llvm-project/issues/161525.


---
Full diff: https://github.com/llvm/llvm-project/pull/161539.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp (+3) 
- (modified) llvm/test/Transforms/InstCombine/fcmp.ll (+40) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index e4cb457499ef5..60da48e1d95d0 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -8527,6 +8527,9 @@ static Instruction *foldFCmpFSubIntoFCmp(FCmpInst &I, Instruction *LHSI,
             DenormalMode::getIEEE()) {
       CI.replaceOperand(I, 0, X);
       CI.replaceOperand(I, 1, Y);
+      I.setHasNoInfs(LHSI->hasNoInfs());
+      if (LHSI->hasNoNaNs())
+        I.setHasNoNaNs(true);
       return &I;
     }
     break;
diff --git a/llvm/test/Transforms/InstCombine/fcmp.ll b/llvm/test/Transforms/InstCombine/fcmp.ll
index 119cffd73c662..d94e78c55a375 100644
--- a/llvm/test/Transforms/InstCombine/fcmp.ll
+++ b/llvm/test/Transforms/InstCombine/fcmp.ll
@@ -1812,6 +1812,46 @@ define i1 @fcmp_ule_fsub_const(float %x, float %y) {
   ret i1 %cmp
 }
 
+define i1 @fcmp_ninf_ule_fsub_const(float %x, float %y) {
+; CHECK-LABEL: @fcmp_ninf_ule_fsub_const(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp ule float [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %fs = fsub float %x, %y
+  %cmp = fcmp ninf ule float %fs, 0.000000e+00
+  ret i1 %cmp
+}
+
+define i1 @fcmp_nnan_ule_fsub_const(float %x, float %y) {
+; CHECK-LABEL: @fcmp_nnan_ule_fsub_const(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp nnan ule float [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %fs = fsub float %x, %y
+  %cmp = fcmp nnan ule float %fs, 0.000000e+00
+  ret i1 %cmp
+}
+
+define i1 @fcmp_ule_fsub_ninf_const(float %x, float %y) {
+; CHECK-LABEL: @fcmp_ule_fsub_ninf_const(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp ninf ule float [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %fs = fsub ninf float %x, %y
+  %cmp = fcmp ule float %fs, 0.000000e+00
+  ret i1 %cmp
+}
+
+define i1 @fcmp_ule_fsub_nnan_const(float %x, float %y) {
+; CHECK-LABEL: @fcmp_ule_fsub_nnan_const(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp nnan ule float [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %fs = fsub nnan float %x, %y
+  %cmp = fcmp ule float %fs, 0.000000e+00
+  ret i1 %cmp
+}
+
 define i1 @fcmp_ugt_fsub_const(float %x, float %y) {
 ; CHECK-LABEL: @fcmp_ugt_fsub_const(
 ; CHECK-NEXT:    [[FS:%.*]] = fsub float [[X:%.*]], [[Y:%.*]]

``````````

</details>


https://github.com/llvm/llvm-project/pull/161539