[LICM] Avoid duplicate work during building AliasSetTracker

Currently we re-use cached info from sub loops or traverse them
to populate AliasSetTracker. But after that we traverse all basic blocks
from the current loop. This is redundant work.

All what we need is traversing the all basic blocks from the loop except
those which are used to get the data from the cache.

This should improve compile time only.

Reviewers: mkazantsev, reames, kariddi, anna
Reviewed By: reames
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D51715

llvm-svn: 341896

1 files changed, 6 insertions, 8 deletions

diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index 4ebe1e39d95..bb918cf717d 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -1535,11 +1535,6 @@ LoopInvariantCodeMotion::collectAliasInfoForLoop(Loop *L, LoopInfo *LI,
                                                  AliasAnalysis *AA) {
   std::unique_ptr<AliasSetTracker> CurAST;
   SmallVector<Loop *, 4> RecomputeLoops;
-  auto mergeLoop = [&CurAST](Loop *L) {
-    // Loop over the body of this loop, looking for calls, invokes, and stores.
-    for (BasicBlock *BB : L->blocks())
-      CurAST->add(*BB); // Incorporate the specified basic block
-  };
   for (Loop *InnerL : L->getSubLoops()) {
     auto MapI = LoopToAliasSetMap.find(InnerL);
     // If the AST for this inner loop is missing it may have been merged into
@@ -1566,10 +1561,13 @@ LoopInvariantCodeMotion::collectAliasInfoForLoop(Loop *L, LoopInfo *LI,
 
   // Add everything from the sub loops that are no longer directly available.
   for (Loop *InnerL : RecomputeLoops)
-    mergeLoop(InnerL);
+    for (BasicBlock *BB : InnerL->blocks())
+      CurAST->add(*BB);
 
-  // And merge in this loop.
-  mergeLoop(L);
+  // And merge in this loop (without anything from inner loops).
+  for (BasicBlock *BB : L->blocks())
+    if (LI->getLoopFor(BB) == L)
+      CurAST->add(*BB);
 
   return CurAST;
 }