ManuelJBrito added a comment.
In D149548#4405173 <https://reviews.llvm.org/D149548#4405173>, @qiucf wrote:
> Why this changes IR output of following case?
>
> // RUN: clang vecpromote.c -S -o - -O0 -target s390x-linux-gnu -fzvector
> -emit-llvm
> #include <vecintrin.h>
>
> vector int si;
> int g;
> int i;
>
> void foo() {
> si = vec_promote(g, i);
> }
>
> // store <4 x i32> undef, ptr %__vec.i, align 16, !noalias !6 ; this undef
> becomes poison after this patch
> // %2 = load i32, ptr %__scalar.addr.i, align 4, !noalias !6
> // %3 = load i32, ptr %__index.addr.i, align 4, !noalias !6
> // %4 = load <4 x i32>, ptr %__vec.i, align 16, !noalias !6
> // %vecins.i = insertelement <4 x i32> %4, i32 %2, i32 %and.i
I think it's because vec_promote is implemented in clang using a shufflevector
with an undefined mask (-1).
ConstantFold sees that we have a fully undefined mask and it folds the
shufflevector to poison.(previously undef)
My concern : is it Ok to have the undefined values of the vector be poison or
was the undef used to abide to some specific semantics?
Hope this makes sense.
> I see no PowerPC related case changes. Maybe adding SystemZ folks for
> comments @uweigand @jonpa
My bad I pinged the wrong people, thanks for adding SystemZ folks.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D149548/new/
https://reviews.llvm.org/D149548
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