https://bugs.llvm.org/show_bug.cgi?id=50123
Bug ID: 50123
Summary: [X86] Failure to recognise generic shift from SSE
PSLLQ intrinsic
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: llvm-...@redking.me.uk
CC: david.bolvan...@gmail.com, lebedev...@gmail.com,
llvm-bugs@lists.llvm.org, nikita....@gmail.com,
spatel+l...@rotateright.com
We often fail to recognise that the _mm_sll_epi64 shift amount is in bounds,
allowing us to fold it to a generic shift. This happens for all SSE 'shift by
uniform variable' intrinsics.
https://simd.godbolt.org/z/vKT9YE5zM
#include <x86intrin.h>
__m128i shl_v2i64_mod31(__m128i val, __m128i amt) {
amt = _mm_and_si128( amt, _mm_set1_epi32( 31 ) );
return _mm_sll_epi64( val, _mm_unpacklo_epi32( amt, _mm_setzero_si128() ) );
}
__m128i shl_v2i64_mod31_alt(__m128i val, __m128i amt) {
amt = _mm_and_si128( amt, _mm_setr_epi32( 31, 0, 0, 0 ) );
return _mm_sll_epi64( val, amt );
}
define <2 x i64> @shl_v2i64_mod31(<2 x i64> %0, <2 x i64> %1){
%3 = bitcast <2 x i64> %1 to <4 x i32>
%4 = and <4 x i32> %3, <i32 31, i32 poison, i32 poison, i32 poison>
%5 = insertelement <4 x i32> %4, i32 0, i32 1
%6 = bitcast <4 x i32> %5 to <2 x i64>
%7 = tail call <2 x i64> @llvm.x86.sse2.psll.q(<2 x i64> %0, <2 x i64> %6)
ret <2 x i64> %7
}
declare <2 x i64> @llvm.x86.sse2.psll.q(<2 x i64>, <2 x i64>)
define <2 x i64> @shl_v2i64_mod31_alt(<2 x i64> %0, <2 x i64> %1) {
%3 = and <2 x i64> %1, <i64 31, i64 poison>
%4 = shufflevector <2 x i64> %3, <2 x i64> poison, <2 x i32> zeroinitializer
%5 = shl <2 x i64> %0, %4
ret <2 x i64> %5
}
I think we're just missing some bitcast/insertelement vector handling in
ValueTracking.
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