Author: Sjoerd Meijer Date: 2020-12-08T11:56:35Z New Revision: 1e260f955d3123351fc68de8c2dde02b1be6d14f
URL: https://github.com/llvm/llvm-project/commit/1e260f955d3123351fc68de8c2dde02b1be6d14f DIFF: https://github.com/llvm/llvm-project/commit/1e260f955d3123351fc68de8c2dde02b1be6d14f.diff LOG: [LICM][docs] Document that LICM is also a canonicalization transform. NFC. This documents that LICM is a canonicalization transform, which we discussed recently in: http://lists.llvm.org/pipermail/llvm-dev/2020-December/147184.html but which was also discused earlier, e.g. in: http://lists.llvm.org/pipermail/llvm-dev/2019-September/135058.html Added: Modified: llvm/docs/Passes.rst llvm/lib/Transforms/Scalar/LICM.cpp Removed: ################################################################################ diff --git a/llvm/docs/Passes.rst b/llvm/docs/Passes.rst index 202e3ab223d6..d146ce745282 100644 --- a/llvm/docs/Passes.rst +++ b/llvm/docs/Passes.rst @@ -720,6 +720,12 @@ into the preheader block, or by sinking code to the exit blocks if it is safe. This pass also promotes must-aliased memory locations in the loop to live in registers, thus hoisting and sinking "invariant" loads and stores. +Hoisting operations out of loops is a canonicalization transform. It enables +and simplifies subsequent optimizations in the middle-end. Rematerialization +of hoisted instructions to reduce register pressure is the responsibility of +the back-end, which has more accurate information about register pressure and +also handles other optimizations than LICM that increase live-ranges. + This pass uses alias analysis for two purposes: #. Moving loop invariant loads and calls out of loops. If we can determine diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp index 9d90986c54ad..1b14bc972a9e 100644 --- a/llvm/lib/Transforms/Scalar/LICM.cpp +++ b/llvm/lib/Transforms/Scalar/LICM.cpp @@ -12,6 +12,13 @@ // safe. This pass also promotes must-aliased memory locations in the loop to // live in registers, thus hoisting and sinking "invariant" loads and stores. // +// Hoisting operations out of loops is a canonicalization transform. It +// enables and simplifies subsequent optimizations in the middle-end. +// Rematerialization of hoisted instructions to reduce register pressure is the +// responsibility of the back-end, which has more accurate information about +// register pressure and also handles other optimizations than LICM that +// increase live-ranges. +// // This pass uses alias analysis for two purposes: // // 1. Moving loop invariant loads and calls out of loops. If we can determine _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
