my instcombine transformations to make extension elimination more
aggressive changed the canonical form from sext(trunc(x)) to ashr(lshr(x)),
make sure to transform a couple more things into that canonical form,
and catch a case where we missed turning zext/shl/ashr into a single sext.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93787 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp
index fe91da1..321c91d 100644
--- a/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -404,12 +404,26 @@
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
// If the input is a SHL by the same constant (ashr (shl X, C), C), then we
- // have a sign-extend idiom. If the input value is known to already be sign
- // extended enough, delete the extension.
+ // have a sign-extend idiom.
Value *X;
- if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1))) &&
- ComputeNumSignBits(X) > Op1C->getZExtValue())
- return ReplaceInstUsesWith(I, X);
+ if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1)))) {
+ // If the input value is known to already be sign extended enough, delete
+ // the extension.
+ if (ComputeNumSignBits(X) > Op1C->getZExtValue())
+ return ReplaceInstUsesWith(I, X);
+
+ // If the input is an extension from the shifted amount value, e.g.
+ // %x = zext i8 %A to i32
+ // %y = shl i32 %x, 24
+ // %z = ashr %y, 24
+ // then turn this into "z = sext i8 A to i32".
+ if (ZExtInst *ZI = dyn_cast<ZExtInst>(X)) {
+ uint32_t SrcBits = ZI->getOperand(0)->getType()->getScalarSizeInBits();
+ uint32_t DestBits = ZI->getType()->getScalarSizeInBits();
+ if (Op1C->getZExtValue() == DestBits-SrcBits)
+ return new SExtInst(ZI->getOperand(0), ZI->getType());
+ }
+ }
}
// See if we can turn a signed shr into an unsigned shr.