Alan Baker 1b6cfd3409 Rewriting dead branch elimination. ... Pass now paints live blocks and fixes constant branches and switches as it goes. No longer requires structured control flow. It also removes unreachable blocks as a side effect. It fixes the IR (phis) before doing any code removal (other than terminator changes). Added several unit tests for updated/new functionality. Does not remove dead edge from a phi node: * Checks that incoming edges are live in order to retain them * Added BasicBlock::IsSuccessor * added test Fixing phi updates in the presence of extra backedge blocks * Added tests to catch bug Reworked how phis are updated * Instead of creating a new Phi and RAUW'ing the old phi with it, I now replace the phi operands, but maintain the def/use manager correctly. For unreachable merge: * When considering unreachable continue blocks the code now properly checks whether the incoming edge will continue to be live. Major refactoring for review * Broke into 4 major functions * marking live blocks * marking structured targets * fixing phis * deleting blocks		2018-01-09 12:21:39 -05:00
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spirv-tools	Rewriting dead branch elimination.	2018-01-09 12:21:39 -05:00