[PATCH] D136201: [InstCombine] Handle PHI nodes when eliminating constant memcpy
Nikita Popov via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Oct 31 09:44:29 PDT 2022
nikic added a comment.
> I believe the change to isOnlyCopiedFromConstantMemory() is fine
I think I spoke too soon ... I can't test this right now, but probably this minor variant is going to be miscompiled:
define i32 @test1(i1 %c, ptr %ptr) {
entry:
%a = alloca [32 x i8]
br i1 %c, label %if, label %join
if:
br label %join
join:
%phi = phi ptr [ %a, %if ], [ %ptr, %entry ]
call void @llvm.memcpy.p0.p0.i64(ptr %phi, ptr @g1, i64 32, i1 false)
%v = load i32, ptr %phi
ret i32 %v
}
While we can replace uses of `%a` with `@g1`, dropping the memcpy would be incorrect, as it would also drop the potential write to `%ptr`, which is not covered by the replacement.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D136201/new/
https://reviews.llvm.org/D136201
More information about the llvm-commits
mailing list