[llvm] [InstCombine] Remove foldSelectWithFrozenICmp() fold (PR #161659)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Nikita Popov (nikic)

<details>
<summary>Changes</summary>

After https://github.com/llvm/llvm-project/pull/154336 this fold no longer triggers, as the freeze will be pushed through to the icmp operands, and generic handling will take care of it.

---
Full diff: https://github.com/llvm/llvm-project/pull/161659.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp (-29) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index b6b3a95f35c76..87000a1c36eef 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -2934,32 +2934,6 @@ static Instruction *foldSelectWithSRem(SelectInst &SI, InstCombinerImpl &IC,
   return nullptr;
 }
 
-static Value *foldSelectWithFrozenICmp(SelectInst &Sel, InstCombiner::BuilderTy &Builder) {
-  FreezeInst *FI = dyn_cast<FreezeInst>(Sel.getCondition());
-  if (!FI)
-    return nullptr;
-
-  Value *Cond = FI->getOperand(0);
-  Value *TrueVal = Sel.getTrueValue(), *FalseVal = Sel.getFalseValue();
-
-  //   select (freeze(x == y)), x, y --> y
-  //   select (freeze(x != y)), x, y --> x
-  // The freeze should be only used by this select. Otherwise, remaining uses of
-  // the freeze can observe a contradictory value.
-  //   c = freeze(x == y)   ; Let's assume that y = poison & x = 42; c is 0 or 1
-  //   a = select c, x, y   ;
-  //   f(a, c)              ; f(poison, 1) cannot happen, but if a is folded
-  //                        ; to y, this can happen.
-  CmpPredicate Pred;
-  if (FI->hasOneUse() &&
-      match(Cond, m_c_ICmp(Pred, m_Specific(TrueVal), m_Specific(FalseVal))) &&
-      (Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE)) {
-    return Pred == ICmpInst::ICMP_EQ ? FalseVal : TrueVal;
-  }
-
-  return nullptr;
-}
-
 /// Given that \p CondVal is known to be \p CondIsTrue, try to simplify \p SI.
 static Value *simplifyNestedSelectsUsingImpliedCond(SelectInst &SI,
                                                     Value *CondVal,
@@ -4446,9 +4420,6 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
   if (Instruction *PN = foldSelectToPhi(SI, DT, Builder))
     return replaceInstUsesWith(SI, PN);
 
-  if (Value *Fr = foldSelectWithFrozenICmp(SI, Builder))
-    return replaceInstUsesWith(SI, Fr);
-
   if (Value *V = foldRoundUpIntegerWithPow2Alignment(SI, Builder))
     return replaceInstUsesWith(SI, V);
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/161659