Fix a performance regression when combining to smaller types in icmp (shl %v, C1), C2 :
Only combine when the shl is only used by the icmp
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176950 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index bad46b4..32fdb9b 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1333,13 +1333,14 @@
}
// Transform (icmp pred iM (shl iM %v, N), CI)
- // -> (icmp pred i(M-N) (trunc %v iM to i(N-N)), (trunc (CI>>N))
- // Transform the shl to a trunc if (trunc (CI>>N)) has no loss.
+ // -> (icmp pred i(M-N) (trunc %v iM to i(M-N)), (trunc (CI>>N))
+ // Transform the shl to a trunc if (trunc (CI>>N)) has no loss and M-N.
// This enables to get rid of the shift in favor of a trunc which can be
// free on the target. It has the additional benefit of comparing to a
// smaller constant, which will be target friendly.
unsigned Amt = ShAmt->getLimitedValue(TypeBits-1);
- if (Amt != 0 && RHSV.countTrailingZeros() >= Amt) {
+ if (LHSI->hasOneUse() &&
+ Amt != 0 && RHSV.countTrailingZeros() >= Amt) {
Type *NTy = IntegerType::get(ICI.getContext(), TypeBits - Amt);
Constant *NCI = ConstantExpr::getTrunc(
ConstantExpr::getAShr(RHS,