[llvm] [X86][DAGCombiner] Skip x87 fp80 values in `combineFMulOrFDivWithIntPow2` (PR #128618)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

f80 is not a valid IEEE floating-point type.
Closes https://github.com/llvm/llvm-project/issues/128528.


---
Full diff: https://github.com/llvm/llvm-project/pull/128618.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (+6-2) 
- (modified) llvm/test/CodeGen/X86/fold-int-pow2-with-fmul-or-fdiv.ll (+28) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index a83be13ebff2b..7347923c7d33d 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -17271,6 +17271,10 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
 // prefer it.
 SDValue DAGCombiner::combineFMulOrFDivWithIntPow2(SDNode *N) {
   EVT VT = N->getValueType(0);
+  if (!Type::getFloatingPointTy(*DAG.getContext(), VT.getFltSemantics())
+           ->isIEEELikeFPTy())
+    return SDValue();
+
   SDValue ConstOp, Pow2Op;
 
   std::optional<int> Mantissa;
@@ -17297,8 +17301,8 @@ SDValue DAGCombiner::combineFMulOrFDivWithIntPow2(SDNode *N) {
 
       const APFloat &APF = CFP->getValueAPF();
 
-      // Make sure we have normal/ieee constant.
-      if (!APF.isNormal() || !APF.isIEEE())
+      // Make sure we have normal constant.
+      if (!APF.isNormal())
         return false;
 
       // Make sure the floats exponent is within the bounds that this transform
diff --git a/llvm/test/CodeGen/X86/fold-int-pow2-with-fmul-or-fdiv.ll b/llvm/test/CodeGen/X86/fold-int-pow2-with-fmul-or-fdiv.ll
index e513b666ebf83..67c9e7cc22236 100644
--- a/llvm/test/CodeGen/X86/fold-int-pow2-with-fmul-or-fdiv.ll
+++ b/llvm/test/CodeGen/X86/fold-int-pow2-with-fmul-or-fdiv.ll
@@ -1688,3 +1688,31 @@ define float @fdiv_pow_shl_cnt32_okay(i32 %cnt) nounwind {
   %mul = fdiv float 0x3a20000000000000, %conv
   ret float %mul
 }
+
+define x86_fp80 @pr128528(i1 %cond) {
+; CHECK-SSE-LABEL: pr128528:
+; CHECK-SSE:       # %bb.0:
+; CHECK-SSE-NEXT:    testb $1, %dil
+; CHECK-SSE-NEXT:    movl $8, %eax
+; CHECK-SSE-NEXT:    movl $1, %ecx
+; CHECK-SSE-NEXT:    cmovnel %eax, %ecx
+; CHECK-SSE-NEXT:    movl %ecx, -{{[0-9]+}}(%rsp)
+; CHECK-SSE-NEXT:    fildl -{{[0-9]+}}(%rsp)
+; CHECK-SSE-NEXT:    fmull {{\.?LCPI[0-9]+_[0-9]+}}(%rip)
+; CHECK-SSE-NEXT:    retq
+;
+; CHECK-AVX-LABEL: pr128528:
+; CHECK-AVX:       # %bb.0:
+; CHECK-AVX-NEXT:    testb $1, %dil
+; CHECK-AVX-NEXT:    movl $8, %eax
+; CHECK-AVX-NEXT:    movl $1, %ecx
+; CHECK-AVX-NEXT:    cmovnel %eax, %ecx
+; CHECK-AVX-NEXT:    movl %ecx, -{{[0-9]+}}(%rsp)
+; CHECK-AVX-NEXT:    fildl -{{[0-9]+}}(%rsp)
+; CHECK-AVX-NEXT:    fmull {{\.?LCPI[0-9]+_[0-9]+}}(%rip)
+; CHECK-AVX-NEXT:    retq
+  %sub9 = select i1 %cond, i32 8, i32 1
+  %conv = uitofp i32 %sub9 to x86_fp80
+  %mul = fmul x86_fp80 %conv, 0xK4007D055555555555800
+  ret x86_fp80 %mul
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/128618