diff options
| -rw-r--r-- | lib/Target/X86/README.txt | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt index af520afe1d..3d9342e2d6 100644 --- a/lib/Target/X86/README.txt +++ b/lib/Target/X86/README.txt @@ -1176,3 +1176,40 @@ andl $65535, %EAX The former can also be used when the two-addressy nature of the 'and' would require a copy to be inserted (in X86InstrInfo::convertToThreeAddress). +//===---------------------------------------------------------------------===// + +This code generates ugly code, probably due to costs being off or something: + +void %test(float* %P, <4 x float>* %P2 ) { + %xFloat0.688 = load float* %P + %loadVector37.712 = load <4 x float>* %P2 + %inFloat3.713 = insertelement <4 x float> %loadVector37.712, float 0.000000e+00, uint 3 + store <4 x float> %inFloat3.713, <4 x float>* %P2 + ret void +} + +Generates: + +_test: + pxor %xmm0, %xmm0 + movd %xmm0, %eax ;; EAX = 0! + movl 8(%esp), %ecx + movaps (%ecx), %xmm0 + pinsrw $6, %eax, %xmm0 + shrl $16, %eax ;; EAX = 0 again! + pinsrw $7, %eax, %xmm0 + movaps %xmm0, (%ecx) + ret + +It would be better to generate: + +_test: + movl 8(%esp), %ecx + movaps (%ecx), %xmm0 + xor %eax, %eax + pinsrw $6, %eax, %xmm0 + pinsrw $7, %eax, %xmm0 + movaps %xmm0, (%ecx) + ret + +or use pxor (to make a zero vector) and shuffle (to insert it). |