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We can't do this for the general case as saying a GEP with a negative index doesn't have unsigned wrap isn't valid for negative indices. %gep = getelementptr inbounds i32* %p, i64 -1 But an inbounds GEP cannot run past the end of address space. So we check for the very common case of a positive index and make GEPs derived from that NUW. Together with Andy's recent non-unit stride work this lets us analyze loops like void foo3(int *a, int *b) { for (; a < b; a++) {} } PR12375, PR12376. Differential Revision: http://llvm-reviews.chandlerc.com/D2033 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193514 91177308-0d34-0410-b5e6-96231b3b80d8
Analysis Opportunities: //===---------------------------------------------------------------------===// In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the ScalarEvolution expression for %r is this: {1,+,3,+,2}<loop> Outside the loop, this could be evaluated simply as (%n * %n), however ScalarEvolution currently evaluates it as (-2 + (2 * (trunc i65 (((zext i64 (-2 + %n) to i65) * (zext i64 (-1 + %n) to i65)) /u 2) to i64)) + (3 * %n)) In addition to being much more complicated, it involves i65 arithmetic, which is very inefficient when expanded into code. //===---------------------------------------------------------------------===// In formatValue in test/CodeGen/X86/lsr-delayed-fold.ll, ScalarEvolution is forming this expression: ((trunc i64 (-1 * %arg5) to i32) + (trunc i64 %arg5 to i32) + (-1 * (trunc i64 undef to i32))) This could be folded to (-1 * (trunc i64 undef to i32)) //===---------------------------------------------------------------------===//