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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal>Hi All,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>In the attached test case there, is an unnested loop with 2 iterations. The loop latch block is terminated by an unconditional branch, so simplifycfg folds the almost empty latch block into its predecessor which is the loop header. This results in an additional backedge in the CFG, so when LoopRotate pass is called it canonicalizes the loop into a nested loop. However, now the loop trip count is unpredictable as the BackedgeTakenCount for the outer loop is not loop invariant. As a result the loop cannot be unrolled. Is this the intended canonicalization for this loop or is the loopsimplify canonicalizing incorrectly? Should simplifycfg skip folding the latch block into the loop header if this results in additional backedges and let the empty blocks be folded during CGP? More details in <a href="https://bugs.llvm.org/show_bug.cgi?id=33605">https://bugs.llvm.org/show_bug.cgi?id=33605</a>.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>FWIW, this prevents unrolling of a hot loop in spec2017/gcc and also prevents loop-interleave of a loop in spec2017/perlbench. Appreciate any suggestions on how to fix this.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Attached testcase:<o:p></o:p></p><p class=MsoNormal>$cat test.c<o:p></o:p></p><p class=MsoNormal>void foo();<o:p></o:p></p><p class=MsoNormal>bool test(int a, int b, int *c) {<o:p></o:p></p><p class=MsoNormal> bool changed = false;<o:p></o:p></p><p class=MsoNormal> for (unsigned int i = 2; i--;) {<o:p></o:p></p><p class=MsoNormal> int r = a | b;<o:p></o:p></p><p class=MsoNormal> if ( r != c[i]) {<o:p></o:p></p><p class=MsoNormal> c[i] = r;<o:p></o:p></p><p class=MsoNormal> foo();<o:p></o:p></p><p class=MsoNormal> changed = true;<o:p></o:p></p><p class=MsoNormal> }<o:p></o:p></p><p class=MsoNormal> }<o:p></o:p></p><p class=MsoNormal> return changed;<o:p></o:p></p><p class=MsoNormal>}<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>Balaram<o:p></o:p></p></div></body></html>