Tweaks to the icmp+sext-to-shifts optimization to address Frits' comments:
- Localize the check if an icmp has one use to a place where we know we're
introducing something that's likely more expensive than a sext from i1.
- Add an assert to make sure a case that would lead to a miscompilation is
folded away earlier.
- Fix a typo.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128744 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 77ad828..5dd6fe5 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -882,10 +882,6 @@
Value *Op0 = ICI->getOperand(0), *Op1 = ICI->getOperand(1);
ICmpInst::Predicate Pred = ICI->getPredicate();
- // Transforming icmps with more than one use is not profitable.
- if (!ICI->hasOneUse())
- return 0;
-
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
// (x <s 0) ? -1 : 0 -> ashr x, 31 -> all ones if signed
// (x >s -1) ? -1 : 0 -> ashr x, 31 -> all ones if not signed
@@ -906,7 +902,8 @@
// If we know that only one bit of the LHS of the icmp can be set and we
// have an equality comparison with zero or a power of 2, we can transform
// the icmp and sext into bitwise/integer operations.
- if (ICI->isEquality() && (Op1C->isZero() || Op1C->getValue().isPowerOf2())){
+ if (ICI->hasOneUse() &&
+ ICI->isEquality() && (Op1C->isZero() || Op1C->getValue().isPowerOf2())){
unsigned BitWidth = Op1C->getType()->getBitWidth();
APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
APInt TypeMask(APInt::getAllOnesValue(BitWidth));
@@ -916,6 +913,9 @@
if (KnownZeroMask.isPowerOf2()) {
Value *In = ICI->getOperand(0);
+ assert((Op1C->isZero() || Op1C->getValue() == KnownZeroMask) &&
+ "Constant icmp not folded?");
+
if (!Op1C->isZero() == (Pred == ICmpInst::ICMP_NE)) {
// sext ((x & 2^n) == 0) -> (x >> n) - 1
// sext ((x & 2^n) != 2^n) -> (x >> n) - 1
@@ -932,7 +932,7 @@
"sext");
} else {
// sext ((x & 2^n) != 0) -> (x << bitwidth-n) a>> bitwidth-1
- // sext ((x & 2^n) != 2^n) -> (x << bitwidth-n) a>> bitwidth-1
+ // sext ((x & 2^n) == 2^n) -> (x << bitwidth-n) a>> bitwidth-1
unsigned ShiftAmt = KnownZeroMask.countLeadingZeros();
// Perform a left shift to place the desired bit in the MSB.
if (ShiftAmt)