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> I am not sure how best to fix this. If possible, InstCombine's canonicalization shouldn't hide arithmetic progressions behind bit masks. At least, it seems these transformations should be disabled unless (X >> C).hasOneUse(). They aren't exactly optimizations. > > This: > >  %div = lshr i32 %a, 2 >  store i32 %div, i32* %p, align 4, !tbaa !0 >  %add = shl

...#39;s see if we have any evidence that reserving this transform for the DAGCombiner hurts things, how it hurts things, and what we can do about it first? -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20120417/0b5e205d/attachment.html>

Look at this silly function: $ cat small.c unsigned f(unsigned a, unsigned *p) { unsigned x = a/4; p[0] = x; p[1] = x+x; return p[1] - 2*p[0]; } GCC turns this into straightforward code and figures out the 0 return value: shrl $2, %edi movl %edi, (%rsi) addl %edi, %edi movl %edi, 4(%rsi) movl $0, %eax ret LLVM optimizes the code: $ clang -O -S -o- small.c -emit-llvm define i32