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Summary: JumpThreading for guards feature has been reverted at https://reviews.llvm.org/rL295200 due to the following problem: the feature used the following algorithm for detection of diamond patters: 1. Find a block with 2 predecessors; 2. Check that these blocks have a common single parent; 3. Check that the parent's terminator is a branch instruction. The problem is that these checks are insufficient. They may pass for a non-diamond construction in case if those two predecessors are actually the same block. This may happen if parent's terminator is a br (either conditional or unconditional) to a block that ends with "switch" instruction with exactly two branches going to one block. This patch re-enables the JumpThreading for guards and fixes this issue by adding the check that those found predecessors are actually different blocks. This guarantees that parent's terminator is a conditional branch with exactly 2 different successors, which is now ensured by assertions. It also adds two more tests for this situation (with parent's terminator being a conditional and an unconditional branch). Patch by Max Kazantsev! Reviewers: anna, sanjoy, reames Reviewed By: sanjoy Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D30036 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295410 91177308-0d34-0410-b5e6-96231b3b80d8
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