[DependenceAnalysis] Dependecies for loads marked with "ivnariant.load" should…

Authored by ebrevnov on Nov 19 2019, 2:26 AM.


[DependenceAnalysis] Dependecies for loads marked with "ivnariant.load" should not be shared with general accesses. Fix for https://bugs.llvm.org/show_bug.cgi?id=42151

Dependence anlysis has a mechanism to cache results. Thus for particular memory access the cache keep track of side effects in basic blocks. The problem is that for invariant loads dependepce analysis legally ignores many dependencies due to a special semantic rules for such loads. But later results calculated for invariant load retrived from the cache for general case acceses. As a result we have wrong dependence information causing GVN to do illegal transformation. Fixes, T42151.

Proposed solution is to disable caching of invariant loads. I think such loads a pretty rare and it doesn't make sense to extend caching mechanism for them.

Reviewers: reames, chandlerc, skatkov, morisset, jdoerfert

Reviewed By: reames

Subscribers: hiraditya, test, jdoerfert, lebedev.ri, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64405