https://bugs.llvm.org/show_bug.cgi?id=39030
Bug ID: 39030
Summary: Inefficient codegen for and(not(shl(shr)))
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: AArch64
Assignee: unassignedb...@nondot.org
Reporter: eugeni.stepa...@gmail.com
CC: llvm-bugs@lists.llvm.org
typedef unsigned long T;
// typedef long T;
T f(T a, T b) {
return b & ~((a >> 56) << 10);
}
With T = long, the source above generates
asr x8, x0, #56
bic x0, x1, x8, lsl #10
ret
With T = unsigned long, we produce much longer code
lsr x8, x0, #46
mvn w8, w8
orr x8, x8, #0xfffffffffffc03ff
and x0, x8, x1
ret
A similar lsr + bic sequence is possible here too, but the BIC pattern does not
match because of the following generic transform (in DAGCombiner.cpp):
// fold (shl (srl x, c1), c2) -> (and (shl x, (sub c2, c1), MASK) or
// (and (srl x, (sub c1, c2), MASK)
Maybe this combine should not be used if it feeds into AND and TLI.hasAndNot()?
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