now that the cost model has changed, we can always consider
elimination of a sign extend to be a win, which simplifies
the client of CanEvaluateSExtd, and allows us to eliminate
more casts (examples taken from real code).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93109 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index b0d017e..13f6071 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -919,34 +919,25 @@
if (NumBitsSExt == 0)
return 0;
+ // Okay, we can transform this! Insert the new expression now.
+ DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type"
+ " to avoid sign extend: " << CI);
+ Value *Res = EvaluateInDifferentType(Src, DestTy, true);
+ assert(Res->getType() == DestTy);
+
uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
uint32_t DestBitSize = DestTy->getScalarSizeInBits();
+
+ // If the high bits are already filled with sign bit, just replace this
+ // cast with the result.
+ if (NumBitsSExt > DestBitSize - SrcBitSize ||
+ ComputeNumSignBits(Res) > DestBitSize - SrcBitSize)
+ return ReplaceInstUsesWith(CI, Res);
- // Because this is a sign extension, we can always transform it by inserting
- // two new shifts (to do the extension). However, this is only profitable
- // if we've eliminated two or more casts from the input. If we know the
- // result will be sign-extended enough to not require these shifts, we can
- // always do the transformation.
- if (NumCastsRemoved >= 2 ||
- NumBitsSExt > DestBitSize-SrcBitSize) {
-
- // Okay, we can transform this! Insert the new expression now.
- DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type"
- " to avoid sign extend: " << CI);
- Value *Res = EvaluateInDifferentType(Src, DestTy, true);
- assert(Res->getType() == DestTy);
-
- // If the high bits are already filled with sign bit, just replace this
- // cast with the result.
- if (NumBitsSExt > DestBitSize - SrcBitSize ||
- ComputeNumSignBits(Res) > DestBitSize - SrcBitSize)
- return ReplaceInstUsesWith(CI, Res);
-
- // We need to emit a shl + ashr to do the sign extend.
- Value *ShAmt = ConstantInt::get(DestTy, DestBitSize-SrcBitSize);
- return BinaryOperator::CreateAShr(Builder->CreateShl(Res, ShAmt, "sext"),
- ShAmt);
- }
+ // We need to emit a shl + ashr to do the sign extend.
+ Value *ShAmt = ConstantInt::get(DestTy, DestBitSize-SrcBitSize);
+ return BinaryOperator::CreateAShr(Builder->CreateShl(Res, ShAmt, "sext"),
+ ShAmt);
}
// If the input is a shl/ashr pair of a same constant, then this is a sign