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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>LLVM supports converting multiplication to shifting and add/sub operations if possible when one operand is a integer variable and the other is a positive constant even if the constant is not power of 2.<o:p></o:p></p><p class=MsoNormal>For example, “x*5” will be converted to “x+x<<2”.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>However, when the constant is a negative and not power of 2, it always emits “mul” even if using shifting+add/sub is possible.<o:p></o:p></p><p class=MsoNormal>For example, “x*-7” should be converted to “x-x<<8” (sub r0, r0, r0, lsl #3 )<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I have reported this into the bugzilla. The URL is <o:p></o:p></p><p class=MsoNormal><a href="http://llvm.org/bugs/show_bug.cgi?id=12212">http://llvm.org/bugs/show_bug.cgi?id=12212</a><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The cause of the issue is in ARMISelLowering.cpp, it treats the constant (“MulAmt”) as uint64_t and therefore it omits the case when MulAmt could be negative.<o:p></o:p></p><p class=MsoNormal>So, I’m providing the fix for this issue. <o:p></o:p></p><p class=MsoNormal>I also run the unit tests and the test suite. My fix doesn't change any result from validtion tests. I believe this is good fix. :D<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I’m attaching the fix (0001-Bug12212-*.patch) and an updated test case (0002-neg-mul-const-unit-test.patch) for such scenario as well as my validation run results (test_results.tar.bz2).<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Please review it.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks,<o:p></o:p></p><p class=MsoNormal>Weiming Zhao<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>