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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Hi, <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>This patch reproduces and fixes an endless loop in Instcombine. The cause of the problem is described below. Please review this patch. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Cheers,<o:p></o:p></p><p class=MsoNormal>Nadav<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Index: llvm/test/Transforms/InstCombine/2011-02-14-InfLoop.ll<o:p></o:p></p><p class=MsoNormal>===================================================================<o:p></o:p></p><p class=MsoNormal>--- llvm/test/Transforms/InstCombine/2011-02-14-InfLoop.ll (revision 0)<o:p></o:p></p><p class=MsoNormal>+++ llvm/test/Transforms/InstCombine/2011-02-14-InfLoop.ll (revision 0)<o:p></o:p></p><p class=MsoNormal>@@ -0,0 +1,17 @@<o:p></o:p></p><p class=MsoNormal>+; This testcase causes an infinite loop in the instruction combiner,<o:p></o:p></p><p class=MsoNormal>+; because it changes a pattern and the original pattern is almost<o:p></o:p></p><p class=MsoNormal>+; identical to the newly-generated pattern.<o:p></o:p></p><p class=MsoNormal>+; RUN: opt < %s -instcombine -disable-output<o:p></o:p></p><p class=MsoNormal>+<o:p></o:p></p><p class=MsoNormal>+target triple = "x86_64-unknown-linux-gnu"<o:p></o:p></p><p class=MsoNormal>+<o:p></o:p></p><p class=MsoNormal>+define <4 x float> @m_387(i8* noalias nocapture %A, i8* nocapture %B, <4 x i1> %C) nounwind {<o:p></o:p></p><p class=MsoNormal>+entry:<o:p></o:p></p><p class=MsoNormal>+ %movcsext20 = sext <4 x i1> %C to <4 x i32><o:p></o:p></p><p class=MsoNormal>+ %tmp2389 = xor <4 x i32> %movcsext20, <i32 -1, i32 -1, i32 -1, i32 -1><o:p></o:p></p><p class=MsoNormal>+ %movcand25 = and <4 x i32> %tmp2389, <i32 undef, i32 undef, i32 undef, i32 -1><o:p></o:p></p><p class=MsoNormal>+ %movcor26 = or <4 x i32> %movcand25, zeroinitializer<o:p></o:p></p><p class=MsoNormal>+ %L2 = bitcast <4 x i32> %movcor26 to <4 x float><o:p></o:p></p><p class=MsoNormal>+ %L3 = shufflevector <4 x float> zeroinitializer, <4 x float> %L2, <4 x i32> <i32 0, i32 1, i32 2, i32 7><o:p></o:p></p><p class=MsoNormal>+ ret <4 x float> %L3<o:p></o:p></p><p class=MsoNormal>+}<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Property changes on: llvm/test/Transforms/InstCombine/2011-02-14-InfLoop.ll<o:p></o:p></p><p class=MsoNormal>___________________________________________________________________<o:p></o:p></p><p class=MsoNormal>Added: svn:eol-style<o:p></o:p></p><p class=MsoNormal> + native<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Index: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp<o:p></o:p></p><p class=MsoNormal>===================================================================<o:p></o:p></p><p class=MsoNormal>--- llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (revision 125511)<o:p></o:p></p><p class=MsoNormal>+++ llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (working copy)<o:p></o:p></p><p class=MsoNormal>@@ -1138,7 +1138,11 @@<o:p></o:p></p><p class=MsoNormal> cast<BinaryOperator>(Op1)->swapOperands();<o:p></o:p></p><p class=MsoNormal> std::swap(A, B);<o:p></o:p></p><p class=MsoNormal> }<o:p></o:p></p><p class=MsoNormal>- if (A == Op0) // A&(A^B) -> A & ~B<o:p></o:p></p><p class=MsoNormal>+ // Notice that the patten (A&(~B)) is actually (A&(-1^B)), so if<o:p></o:p></p><p class=MsoNormal>+ // A is originally -1 (or a vector of -1 and undefs), then we enter<o:p></o:p></p><p class=MsoNormal>+ // an endless loop. By checking that A is non-constant we ensure that<o:p></o:p></p><p class=MsoNormal>+ // we will never get to the loop.<o:p></o:p></p><p class=MsoNormal>+ if (A == Op0 && ! dyn_cast<Constant>(A) ) // A&(A^B) -> A & ~B<o:p></o:p></p><p class=MsoNormal> return BinaryOperator::CreateAnd(A, Builder->CreateNot(B, "tmp"));<o:p></o:p></p><p class=MsoNormal> }<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div><font face="monospace">---------------------------------------------------------------------<br>
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