[llvm-branch-commits] [llvm] release/20.x: [X86][DAGCombiner] Skip x87 fp80 values in `combineFMulOrFDivWithIntPow2` (#128618) (PR #128717)

[via llvm-branch-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-support

Author: None (llvmbot)

<details>
<summary>Changes</summary>

Backport 44d1dbd24c20a0ee93063dcf44d68e2b8f0bf77c

Requested by: @<!-- -->dtcxzyw

---
Full diff: https://github.com/llvm/llvm-project/pull/128717.diff


4 Files Affected:

- (modified) llvm/include/llvm/ADT/APFloat.h (+1) 
- (modified) llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (+5-2) 
- (modified) llvm/lib/Support/APFloat.cpp (+5) 
- (modified) llvm/test/CodeGen/X86/fold-int-pow2-with-fmul-or-fdiv.ll (+28) 


``````````diff
diff --git a/llvm/include/llvm/ADT/APFloat.h b/llvm/include/llvm/ADT/APFloat.h
index 9792749230cbf..3bff205e7aa9e 100644
--- a/llvm/include/llvm/ADT/APFloat.h
+++ b/llvm/include/llvm/ADT/APFloat.h
@@ -353,6 +353,7 @@ struct APFloatBase {
   static bool semanticsHasSignedRepr(const fltSemantics &);
   static bool semanticsHasInf(const fltSemantics &);
   static bool semanticsHasNaN(const fltSemantics &);
+  static bool isIEEELikeFP(const fltSemantics &);
 
   // Returns true if any number described by \p Src can be precisely represented
   // by a normal (not subnormal) value in \p Dst.
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index a0c703d2df8a2..d57766cd9a5bc 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -17281,6 +17281,9 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
 // prefer it.
 SDValue DAGCombiner::combineFMulOrFDivWithIntPow2(SDNode *N) {
   EVT VT = N->getValueType(0);
+  if (!APFloat::isIEEELikeFP(VT.getFltSemantics()))
+    return SDValue();
+
   SDValue ConstOp, Pow2Op;
 
   std::optional<int> Mantissa;
@@ -17307,8 +17310,8 @@ 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/lib/Support/APFloat.cpp b/llvm/lib/Support/APFloat.cpp
index b0d92ae37fe8f..cbee7f48b8773 100644
--- a/llvm/lib/Support/APFloat.cpp
+++ b/llvm/lib/Support/APFloat.cpp
@@ -353,6 +353,11 @@ bool APFloatBase::semanticsHasNaN(const fltSemantics &semantics) {
   return semantics.nonFiniteBehavior != fltNonfiniteBehavior::FiniteOnly;
 }
 
+bool APFloatBase::isIEEELikeFP(const fltSemantics &semantics) {
+  // Keep in sync with Type::isIEEELikeFPTy
+  return SemanticsToEnum(semantics) <= S_IEEEquad;
+}
+
 bool APFloatBase::isRepresentableAsNormalIn(const fltSemantics &Src,
                                             const fltSemantics &Dst) {
   // Exponent range must be larger.
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 2163121410553..15a9cbecd808a 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
@@ -1662,3 +1662,31 @@ 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/128717