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In r263618, JumpThreading learned to look trough simple cast instructions, but only if the source of those cast instructions was a phi/cmp i1 (in an effort to limit compile time effects). I think this condition is too restrictive. For switches with limited value range, InstCombine will readily introduce an extra trunc instruction to a smaller integer type (e.g. from i8 to i2), leaving us in the somewhat perverse situation that jump-threading would work before running instcombine, but not after. Since instcombine produces this pattern, I think we need to consider it canonical and support it in JumpThreading. In general, for limiting recursion, I think the existing restriction to phi and cmp nodes should be sufficient to avoid looking through unprofitable chains of instructions. Patch by Keno Fischer! Differential Revision: https://reviews.llvm.org/D42262 llvm-svn: 327150
Low Level Virtual Machine (LLVM)
This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments.