two changes:
1) don't try to optimize a sext or zext that is only used by a trunc, let
the trunc get optimized first. This avoids some pointless effort in
some common cases since instcombine scans down a block in the first pass.
2) Change the cost model for zext elimination to consider an 'and' cheaper
than a zext. This allows us to do it more aggressively, and for the next
patch to simplify the code quite a bit.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93097 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 3ad786b..34937ab 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -695,6 +695,11 @@
}
Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
+ // If this zero extend is only used by a truncate, let the truncate by
+ // eliminated before we try to optimize this zext.
+ if (CI.hasOneUse() && isa<TruncInst>(CI.use_back()))
+ return 0;
+
// If one of the common conversion will work, do it.
if (Instruction *Result = commonCastTransforms(CI))
return Result;
@@ -716,33 +721,25 @@
int BitsZExt = CanEvaluateZExtd(Src, DestTy, NumCastsRemoved, TD);
if (BitsZExt == -1) return 0;
+ // Okay, we can transform this! Insert the new expression now.
+ DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type"
+ " to avoid zero extend: " << CI);
+ Value *Res = EvaluateInDifferentType(Src, DestTy, false);
+ assert(Res->getType() == DestTy);
+
+ // If the high bits are already filled with zeros, just replace this
+ // cast with the result.
uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
uint32_t DestBitSize = DestTy->getScalarSizeInBits();
-
- // If this is a zero-extension, we need to do an AND to maintain the clear
- // top-part of the computation. If we know the result will be zero
- // extended enough already, we don't need the and.
- if (NumCastsRemoved >= 1 ||
- unsigned(BitsZExt) >= DestBitSize-SrcBitSize) {
-
- // Okay, we can transform this! Insert the new expression now.
- DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type"
- " to avoid zero extend: " << CI);
- Value *Res = EvaluateInDifferentType(Src, DestTy, false);
- assert(Res->getType() == DestTy);
-
- // If the high bits are already filled with zeros, just replace this
- // cast with the result.
- if (unsigned(BitsZExt) >= DestBitSize-SrcBitSize ||
- MaskedValueIsZero(Res, APInt::getHighBitsSet(DestBitSize,
- DestBitSize-SrcBitSize)))
- return ReplaceInstUsesWith(CI, Res);
-
- // We need to emit an AND to clear the high bits.
- Constant *C = ConstantInt::get(CI.getContext(),
- APInt::getLowBitsSet(DestBitSize, SrcBitSize));
- return BinaryOperator::CreateAnd(Res, C);
- }
+ if (unsigned(BitsZExt) >= DestBitSize-SrcBitSize ||
+ MaskedValueIsZero(Res, APInt::getHighBitsSet(DestBitSize,
+ DestBitSize-SrcBitSize)))
+ return ReplaceInstUsesWith(CI, Res);
+
+ // We need to emit an AND to clear the high bits.
+ Constant *C = ConstantInt::get(CI.getContext(),
+ APInt::getLowBitsSet(DestBitSize, SrcBitSize));
+ return BinaryOperator::CreateAnd(Res, C);
}
// If this is a TRUNC followed by a ZEXT then we are dealing with integral
@@ -951,6 +948,11 @@
}
Instruction *InstCombiner::visitSExt(SExtInst &CI) {
+ // If this sign extend is only used by a truncate, let the truncate by
+ // eliminated before we try to optimize this zext.
+ if (CI.hasOneUse() && isa<TruncInst>(CI.use_back()))
+ return 0;
+
if (Instruction *I = commonCastTransforms(CI))
return I;