Sanjoy Das 479a57ca4a New pass: guard widening ... Summary: Implement guard widening in LLVM. Description from GuardWidening.cpp: The semantics of the `@llvm.experimental.guard` intrinsic lets LLVM transform it so that it fails more often that it did before the transform. This optimization is called "widening" and can be used hoist and common runtime checks in situations like these: ``` %cmp0 = 7 u< Length call @llvm.experimental.guard(i1 %cmp0) [ "deopt"(...) ] call @unknown_side_effects() %cmp1 = 9 u< Length call @llvm.experimental.guard(i1 %cmp1) [ "deopt"(...) ] ... ``` to ``` %cmp0 = 9 u< Length call @llvm.experimental.guard(i1 %cmp0) [ "deopt"(...) ] call @unknown_side_effects() ... ``` If `%cmp0` is false, `@llvm.experimental.guard` will "deoptimize" back to a generic implementation of the same function, which will have the correct semantics from that point onward. It is always _legal_ to deoptimize (so replacing `%cmp0` with false is "correct"), though it may not always be profitable to do so. NB! This pass is a work in progress. It hasn't been tuned to be "production ready" yet. It is known to have quadriatic running time and will not scale to large numbers of guards Reviewers: reames, atrick, bogner, apilipenko, nlewycky Subscribers: mcrosier, llvm-commits Differential Revision: http://reviews.llvm.org/D20143 llvm-svn: 269997		2016-05-18 22:55:34 +00:00
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CMakeLists.txt
LLVMBuild.txt	Fix shared build of LLVMPasses.	2016-04-18 19:04:19 +00:00
PassBuilder.cpp	New pass: guard widening	2016-05-18 22:55:34 +00:00
PassRegistry.def	New pass: guard widening	2016-05-18 22:55:34 +00:00