| Issue |
66191
|
| Summary |
[X86] Poor movmskps bit extraction
|
| Labels |
backend:X86,
llvm:SelectionDAG
|
| Assignees |
|
| Reporter |
RKSimon
|
```c
#include <x86intrin.h>
void func();
void scatter_mask_vector_i32_epi32(__m128 mask) {
if (_mm_movemask_ps(mask) & 0x8)
func();
}
```
is optimized to the following ir:
```ll
define void @scatter_mask_vector_i32_epi32(<4 x float> noundef %mask) {
entry:
%0 = bitcast <4 x float> %mask to <4 x i32>
%1 = icmp slt <4 x i32> %0, zeroinitializer
%2 = bitcast <4 x i1> %1 to i4
%tobool.not = icmp sgt i4 %2, -1
br i1 %tobool.not, label %if.end, label %if.then
if.then:
tail call void @func()()
br label %if.end
if.end:
ret void
}
declare void @func()() local_unnamed_addr
```
```asm
scatter_mask_vector_i32_epi32:
vmovmskps %xmm0, %eax
shlb $4, %al
sarb $4, %al
js func()@PLT # TAILCALL
retq
```
Changing the bit test to a lower bit in the mask creates much simpler code:
```c
#include <x86intrin.h>
void func();
void scatter_mask_vector_i32_epi32(__m128 mask) {
if (_mm_movemask_ps(mask) & 0x2)
func();
}
```
```ll
define void @scatter_mask_vector_i32_epi32(<4 x float> noundef %mask) {
entry:
%0 = bitcast <4 x float> %mask to <4 x i32>
%1 = icmp slt <4 x i32> %0, zeroinitializer
%2 = bitcast <4 x i1> %1 to i4
%3 = and i4 %2, 2
%tobool.not = icmp eq i4 %3, 0
br i1 %tobool.not, label %if.end, label %if.then
if.then:
tail call void @func()()
br label %if.end
if.end:
ret void
}
declare void @func()() local_unnamed_addr #1
```
```asm
scatter_mask_vector_i32_epi32:
vmovmskps %xmm0, %eax
testb $2, %al
jne func()@PLT # TAILCALL
retq
```
With suitable value tracking we should be able to convert the i4 sext_inreg into a signbit test on the source mask value.
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