[llvm] [SimplifyCFG] Add optimization for switches of powers of two (PR #70977)

[Nikita Popov via llvm-commits]

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@@ -6839,6 +6836,74 @@ static bool ReduceSwitchRange(SwitchInst *SI, IRBuilder<> &Builder,
   return true;
 }
 
+static bool simplifySwitchOfPowersOfTwo(SwitchInst *SI, IRBuilder<> &Builder,
+                                        const DataLayout &DL,
+                                        const TargetTransformInfo &TTI) {
+
+  Value *Condition = SI->getCondition();
+  LLVMContext &Context = SI->getContext();
+  auto *CondTy = cast<IntegerType>(Condition->getType());
+
+  if (CondTy->getIntegerBitWidth() > 64 ||
+      !DL.fitsInLegalInteger(CondTy->getIntegerBitWidth()))
+    return false;
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nikic wrote:

Can you please add a negative test with i128 condition type?

https://github.com/llvm/llvm-project/pull/70977