[CodeExtractor] Factor out and reuse shrinkwrap analysis
Factor out CodeExtractor's analysis of allocas (for shrinkwrapping
purposes), and allow the analysis to be reused.
This resolves a quadratic compile-time bug observed when compiling
AMDGPUDisassembler.cpp.o.
Pre-patch (Release + LTO clang):
```
---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
176.5278 ( 57.8%) 0.4915 ( 18.5%) 177.0192 ( 57.4%) 177.4112 ( 57.3%) Hot Cold Splitting
```
Post-patch (ReleaseAsserts clang):
```
---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
1.4051 ( 3.3%) 0.0079 ( 0.3%) 1.4129 ( 3.2%) 1.4129 ( 3.2%) Hot Cold Splitting
```
Testing: check-llvm, and comparing the AMDGPUDisassembler.cpp.o binary
pre- vs. post-patch.
An alternate approach is to hide CodeExtractorAnalysisCache from clients
of CodeExtractor, and to recompute the analysis from scratch inside of
CodeExtractor::extractCodeRegion(). This eliminates some redundant work
in the shrinkwrapping legality check. However, some clients continue to
exhibit O(n^2) compile time behavior as computing the analysis is O(n).
rdar://55912966
Differential Revision: https://reviews.llvm.org/D68616
llvm-svn: 374089
diff --git a/llvm/lib/Transforms/IPO/BlockExtractor.cpp b/llvm/lib/Transforms/IPO/BlockExtractor.cpp
index 56854fc..de80c88 100644
--- a/llvm/lib/Transforms/IPO/BlockExtractor.cpp
+++ b/llvm/lib/Transforms/IPO/BlockExtractor.cpp
@@ -206,7 +206,8 @@
++NumExtracted;
Changed = true;
}
- Function *F = CodeExtractor(BlocksToExtractVec).extractCodeRegion();
+ CodeExtractorAnalysisCache CEAC(*BBs[0]->getParent());
+ Function *F = CodeExtractor(BlocksToExtractVec).extractCodeRegion(CEAC);
if (F)
LLVM_DEBUG(dbgs() << "Extracted group '" << (*BBs.begin())->getName()
<< "' in: " << F->getName() << '\n');