Transform: "icmp eq (trunc (lshr(X, cst1)), cst" to "icmp (and X, mask), cst"
when X has multiple uses. This is useful for exposing secondary optimizations,
but the X86 backend isn't ready for this when X has a single use. For example,
this can disable load folding.
This is inching towards resolving PR6627.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130238 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 5057154..bb9b88b 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2506,6 +2506,31 @@
}
}
+ // Transform "icmp eq (trunc (lshr(X, cst1)), cst" to
+ // "icmp (and X, mask), cst"
+ uint64_t ShAmt = 0;
+ ConstantInt *Cst1;
+ if (Op0->hasOneUse() &&
+ match(Op0, m_Trunc(m_OneUse(m_LShr(m_Value(A),
+ m_ConstantInt(ShAmt))))) &&
+ match(Op1, m_ConstantInt(Cst1)) &&
+ // Only do this when A has multiple uses. This is most important to do
+ // when it exposes other optimizations.
+ !A->hasOneUse()) {
+ unsigned ASize =cast<IntegerType>(A->getType())->getPrimitiveSizeInBits();
+
+ if (ShAmt < ASize) {
+ APInt MaskV =
+ APInt::getLowBitsSet(ASize, Op0->getType()->getPrimitiveSizeInBits());
+ MaskV <<= ShAmt;
+
+ APInt CmpV = Cst1->getValue().zext(ASize);
+ CmpV <<= ShAmt;
+
+ Value *Mask = Builder->CreateAnd(A, Builder->getInt(MaskV));
+ return new ICmpInst(I.getPredicate(), Mask, Builder->getInt(CmpV));
+ }
+ }
}
{