Andrew Trick a5c5bc9948 SCEV should use NSW to get trip count for positive nonunit stride loops. ... SCEV currently fails to compute loop counts for nonunit stride loops. This comes up frequently. It prevents loop optimization and forces vectorization to insert extra loop checks. For example: void foo(int n, int *x) { for (int i = 0; i < n; i += 3) { x[i] = i; x[i+1] = i+1; x[i+2] = i+2; } } We need to properly handle the case in which limit > INT_MAX-stride. In the above case: n > INT_MAX-3. In this case the loop counter will step beyond the limit and overflow at the same time. However, knowing that signed integer overlow in undefined, we can assume the loop test behavior is arbitrary after overflow. This obeys both C undefined behavior rules, and the more strict LLVM poison value rules. I'm finally fixing this in response to Hal Finkel's persistence. The most probable reason that we never optimized this before is that we were being careful to handle case where the developer expected a side-effect free infinite loop relying on overflow: for (int i = 0; i < n; i += s) { ++j; } return j; If INT_MAX+1 is a multiple of s and n > INT_MAX-s, then we might expect an infinite loop. However there are plenty of ways to achieve this effect without relying on undefined behavior of signed overflow. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193015 91177308-0d34-0410-b5e6-96231b3b80d8		2013-10-18 23:43:53 +00:00
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BasicAA	Use CHECK-LABEL	2013-09-30 23:31:55 +00:00
BlockFrequencyInfo
BranchProbabilityInfo
CallGraph
CostModel
DependenceAnalysis
Dominators
GlobalsModRef
Lint
LoopInfo
MemoryDependenceAnalysis
PostDominators
RegionInfo
ScalarEvolution	SCEV should use NSW to get trip count for positive nonunit stride loops.	2013-10-18 23:43:53 +00:00
TypeBasedAliasAnalysis	TBAA: handle scalar TBAA format and struct-path aware TBAA format.	2013-09-27 18:34:27 +00:00