forked from OSchip/llvm-project
f29dfd36bb
This contains a fix for the issue that caused the revert: we no longer assume that we can insert instructions after the instruction that produces the base pointer. We previously assumed that this would be ok, because the instruction produces a value and therefore is not a terminator. This is false for invoke instructions. We will now insert these new instruction directly at the location of the users. Original commit message: [InstCombine] Look through PHIs, GEPs, IntToPtrs and PtrToInts to expose more constants when comparing GEPs Summary: When comparing two GEP instructions which have the same base pointer and one of them has a constant index, it is possible to only compare indices, transforming it to a compare with a constant. This removes one use for the GEP instruction with the constant index, can reduce register pressure and can sometimes lead to removing the comparisson entirely. InstCombine was already doing this when comparing two GEPs if the base pointers were the same. However, in the case where we have complex pointer arithmetic (GEPs applied to GEPs, PHIs of GEPs, conversions to or from integers, etc) the value of the original base pointer will be hidden to the optimizer and this transformation will be disabled. This change detects when the two sides of the comparison can be expressed as GEPs with the same base pointer, even if they don't appear as such in the IR. The transformation will convert all the pointer arithmetic to arithmetic done on indices and all the relevant uses of GEPs to GEPs with a common base pointer. The GEP comparison will be converted to a comparison done on indices. Reviewers: majnemer, jmolloy Subscribers: hfinkel, jevinskie, jmolloy, aadg, llvm-commits Differential Revision: http://reviews.llvm.org/D15146 llvm-svn: 257897 |
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README.txt
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. LLVM is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. Please see the documentation provided in docs/ for further assistance with LLVM, and in particular docs/GettingStarted.rst for getting started with LLVM and docs/README.txt for an overview of LLVM's documentation setup. If you are writing a package for LLVM, see docs/Packaging.rst for our suggestions.