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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Hello,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I worked on an LLVM patch to optimize integer ABS idiom for the ARM target and would like to submit it to your review.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I experimented with EEMBC benchmarks, in particular MPEG encoding, and noted integer ABS computation happens frequently. Significant speed up was achieved with the optimized idiom for ARM (20% for MPEG encoding).<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><b>Patch details:<o:p></o:p></b></p><p class=MsoNormal><b><o:p> </o:p></b></p><p class=MsoNormal>LLVM lowers SELECT_CC nodes that represent an integer ABS pattern into ASR/ADD/XOR instructions. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>It is possible to create an optimized machine idiom for integer ABS on ARM formed by MOVs/RSBmi predicated instructions.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>This patch modifies ARM-specific files to implement the above optimized machine idiom for integer ABS.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Generation of the optimized integer ABS idiom is turned on by default. To turn this feature off set -disable-arm-int-abs feature flag.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>abspatch.diff <o:p></o:p></p><p class=MsoNormal>Changes to ARM-specific files to implement optimized integer ABS idiom.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>abstestpatch.diff <o:p></o:p></p><p class=MsoNormal>ARM/iabs.ll and Thumb/iabs.ll tests check for the non-optimized integer ABS idiom (ASR/ADD/XOR).<o:p></o:p></p><p class=MsoNormal>When applying abspatch.diff these tests fail. So patched the tests to set -disable-arm-int-abs flag to prevent the compiler from generating optimized integer ABS pattern and allow the non-optimized idiom to be checked.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>iabsopt.ll <o:p></o:p></p><p class=MsoNormal>Similar to ARM/iabs.ll and Thumb/iabs.ll tests except that it checks for the optimized integer ABS idiom and checks for all possible test conditions.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>failures.txt<o:p></o:p></p><p class=MsoNormal>Failure report and explanation from running llvm/test and projects/test-suite on ARM.<o:p></o:p></p><p class=MsoNormal>I noted failures running llvm/test (svn version 139318) and projects/test-suite (svn revision 139319) on ARM. Are these failures expected?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thank you,<o:p></o:p></p><p class=MsoNormal>Ana.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>