[llvm] [SimplifyCFG] Transform switch to select when common bits uniquely identify one case (PR #145233)
Yingwei Zheng via llvm-commits
llvm-commits at lists.llvm.org
Mon Jun 30 02:37:35 PDT 2025
================
@@ -6234,10 +6234,34 @@ static Value *foldSwitchToSelect(const SwitchCaseResultVectorTy &ResultVector,
// case 0,2,8,10 -> Cond & 0b1..0101 == 0 ? result : default
if (isPowerOf2_32(CaseCount)) {
ConstantInt *MinCaseVal = CaseValues[0];
- // Find mininal value.
- for (auto *Case : CaseValues)
+ // In case, there are bits, that can only be present in the CaseValues we
+ // can transform the switch into a select if the conjunction of
+ // all the values uniquely identify the CaseValues.
+ APInt AndMask = APInt::getAllOnes(MinCaseVal->getBitWidth());
+
+ for (auto *Case : CaseValues) {
if (Case->getValue().slt(MinCaseVal->getValue()))
MinCaseVal = Case;
+ AndMask &= Case->getValue();
+ }
+
+ KnownBits Known = computeKnownBits(Condition, DL);
+ unsigned int ConditionWidth = Condition->getType()->getIntegerBitWidth();
+ APInt ActiveBits = APInt(ConditionWidth, Known.countMaxActiveBits(),
+ Condition->getType()->isSingleValueType());
----------------
dtcxzyw wrote:
```suggestion
Condition->getType()->isSingleValueType());
```
It is evaluated as `true`. But it should be treated as an unsigned value.
https://github.com/llvm/llvm-project/pull/145233
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