forked from OSchip/llvm-project
ae945e7927
This is an extension of the shuffle combining from r203229: http://reviews.llvm.org/rL203229 The idea is to widen a short input vector with undef elements so the existing shuffle transform for extract/insert can kick in. The motivation is to finally solve PR2109: https://llvm.org/bugs/show_bug.cgi?id=2109 For that example, the IR becomes: %1 = bitcast <2 x i32>* %P to <2 x float>* %ld1 = load <2 x float>, <2 x float>* %1, align 8 %2 = shufflevector <2 x float> %ld1, <2 x float> undef, <4 x i32> <i32 0, i32 1, i32 undef, i32 undef> %i2 = shufflevector <4 x float> %A, <4 x float> %2, <4 x i32> <i32 0, i32 1, i32 4, i32 5> ret <4 x float> %i2 And x86 SSE output improves from: movq (%rdi), %xmm1 ## xmm1 = mem[0],zero movdqa %xmm1, %xmm2 shufps $229, %xmm2, %xmm2 ## xmm2 = xmm2[1,1,2,3] shufps $48, %xmm0, %xmm1 ## xmm1 = xmm1[0,0],xmm0[3,0] shufps $132, %xmm1, %xmm0 ## xmm0 = xmm0[0,1],xmm1[0,2] shufps $32, %xmm0, %xmm2 ## xmm2 = xmm2[0,0],xmm0[2,0] shufps $36, %xmm2, %xmm0 ## xmm0 = xmm0[0,1],xmm2[2,0] retq To the almost optimal: movhpd (%rdi), %xmm0 Note: There's a tension in the existing transform related to generating arbitrary shufflevector masks. We avoid that in other places in InstCombine because we're scared that codegen can't handle strange masks, but it looks like we're ok with producing those here. I purposely chose weird insert/extract indexes for the regression tests to see the effect in these cases. For PowerPC+Altivec, AArch64, and X86+SSE/AVX, I think the codegen is equal or better for these examples. Differential Revision: http://reviews.llvm.org/D15096 llvm-svn: 256394 |
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README.txt
Low Level Virtual Machine (LLVM) ================================ This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments. LLVM is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. Please see the documentation provided in docs/ for further assistance with LLVM, and in particular docs/GettingStarted.rst for getting started with LLVM and docs/README.txt for an overview of LLVM's documentation setup. If you are writing a package for LLVM, see docs/Packaging.rst for our suggestions.