[InstCombine] reduce funnel-shift i16 X, X, 8 to bswap X
Prefer the more exact intrinsic to remove a use of the input value
and possibly make further transforms easier (we will still need
to match patterns with funnel-shift of wider types as pieces of
bswap, especially if we want to canonicalize to funnel-shift with
constant shift amount). Discussed in D46760.
llvm-svn: 364187
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 1b24724..63f313e 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1983,6 +1983,13 @@
if (match(Op0, m_ZeroInt()) || match(Op0, m_Undef()))
return BinaryOperator::CreateLShr(Op1,
ConstantExpr::getSub(WidthC, ShAmtC));
+
+ // fshl i16 X, X, 8 --> bswap i16 X (reduce to more-specific form)
+ if (Op0 == Op1 && BitWidth == 16 && match(ShAmtC, m_SpecificInt(8))) {
+ Module *Mod = II->getModule();
+ Function *Bswap = Intrinsic::getDeclaration(Mod, Intrinsic::bswap, Ty);
+ return CallInst::Create(Bswap, { Op0 });
+ }
}
// Left or right might be masked.