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Summary: In RewriteLoopExitValues, before expanding out an SCEV expression using SCEVExpander, try to see if an existing LLVM IR expression already computes the value we're interested in. If so use that existing expression. Apart from reducing IndVars' reliance on the rest of the compilation pipeline, this also prevents IndVars from concluding some expressions as "high cost" when they're not. For instance, `InductiveRangeCheckElimination` often emits code of the following form: ``` len = umin(len_A, len_B) loop: ... if (i++ < len) goto loop outside_loop: use(i) ``` `SCEVExpander` refuses to rewrite the use of `i` in `outside_loop`, since it thinks the value of `i` on loop exit, `len`, is a high cost expansion since it contains an `umax` in it. With this change, `IndVars` can see that it can re-use `len` instead of creating a new expression to compute `umin(len_A, len_B)`. I considered putting this cleverness in `SCEVExpander`, but I was worried that it may then have a deterimental effect on other passes that use it. So I decided it was better to just do this in the one place where it seems like an obviously good idea, with the intent of generalizing later if needed. Reviewers: atrick, reames Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D10782 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241838 91177308-0d34-0410-b5e6-96231b3b80d8 |
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Hello | ||
InstCombine | ||
Instrumentation | ||
IPO | ||
ObjCARC | ||
Scalar | ||
Utils | ||
Vectorize | ||
CMakeLists.txt | ||
LLVMBuild.txt | ||
Makefile |