[llvm] [SimplifyCFG]: Switch on umin replaces default (PR #164097)

[Hongyu Chen via llvm-commits]

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@@ -7540,6 +7540,62 @@ static bool reduceSwitchRange(SwitchInst *SI, IRBuilder<> &Builder,
   return true;
 }
 
+/// Tries to transform the switch when the condition is umin and a constant.
+/// In that case, the default branch can be replaced by the constant's branch.
+/// For example:
+/// switch(umin(a, 3)) {
+/// case 0:
+/// case 1:
+/// case 2:
+/// case 3:
+///   // ...
+/// default:
+///   unreachable
+/// }
+///
+/// Transforms into:
+///
+/// switch(umin(a, 3)) {
+/// case 0:
+/// case 1:
+/// case 2:
+/// default:
+///   // This is case 3
+/// }
+static bool simplifySwitchWhenUMin(SwitchInst *SI, IRBuilder<> &Builder) {
+  auto *Call = dyn_cast<IntrinsicInst>(SI->getCondition());
+
+  if (!Call)
+    return false;
+
+  if (Call->getIntrinsicID() != Intrinsic::umin)
+    return false;
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XChy wrote:

Use `match(m_UMin(m_Value(), m_ConstantInt(Constant)))` instead?

https://github.com/llvm/llvm-project/pull/164097