Add a small missed optimization: turn X == C ? X : Y into X == C ? C : Y. This
removes one use of X which helps it pass the many hasOneUse() checks.
In my analysis, this turns up very often where X = A >>exact B and that can't be
simplified unless X has one use (except by increasing the lifetime of A which is
generally a performance loss).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128373 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 8b9261b..50ea79f 100644
--- a/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -424,6 +424,19 @@
return ReplaceInstUsesWith(SI, TrueVal);
/// NOTE: if we wanted to, this is where to detect integer MIN/MAX
}
+
+ if (isa<Constant>(CmpRHS)) {
+ if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
+ // Transform (X == C) ? X : Y -> (X == C) ? C : Y
+ SI.setOperand(1, CmpRHS);
+ Changed = true;
+ } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
+ // Transform (X != C) ? Y : X -> (X != C) ? Y : C
+ SI.setOperand(2, CmpRHS);
+ Changed = true;
+ }
+ }
+
return Changed ? &SI : 0;
}