[asan] Speed up compilation of large C++ stringmaps (tons of allocas) with ASan

This addresses PR30746, <https://llvm.org/bugs/show_bug.cgi?id=30746>. The ASan pass iterates over entry-block instructions and checks each alloca whether it's in NonInstrumentedStaticAllocaVec, which is apparently slow. This patch gathers the instructions to move during visitAllocaInst.

Differential Revision: https://reviews.llvm.org/D26380

llvm-svn: 286296

1 files changed, 12 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
index df068e88090..e4873135dc1 100644
--- a/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -638,7 +638,7 @@ struct FunctionStackPoisoner : public InstVisitor<FunctionStackPoisoner> {
   ShadowMapping Mapping;
 
   SmallVector<AllocaInst *, 16> AllocaVec;
-  SmallSetVector<AllocaInst *, 16> NonInstrumentedStaticAllocaVec;
+  SmallVector<AllocaInst *, 16> StaticAllocasToMoveUp;
   SmallVector<Instruction *, 8> RetVec;
   unsigned StackAlignment;
 
@@ -766,7 +766,14 @@ struct FunctionStackPoisoner : public InstVisitor<FunctionStackPoisoner> {
   /// \brief Collect Alloca instructions we want (and can) handle.
   void visitAllocaInst(AllocaInst &AI) {
     if (!ASan.isInterestingAlloca(AI)) {
-      if (AI.isStaticAlloca()) NonInstrumentedStaticAllocaVec.insert(&AI);
+      if (AI.isStaticAlloca()) {
+        // Skip over allocas that are present *before* the first instrumented
+        // alloca, we don't want to move those around.
+        if (AllocaVec.empty())
+          return;
+
+        StaticAllocasToMoveUp.push_back(&AI);
+      }
       return;
     }
 
@@ -2231,10 +2238,9 @@ void FunctionStackPoisoner::processStaticAllocas() {
   // regular stack slots.
   auto InsBeforeB = InsBefore->getParent();
   assert(InsBeforeB == &F.getEntryBlock());
-  for (BasicBlock::iterator I(InsBefore); I != InsBeforeB->end(); ++I)
-    if (auto *AI = dyn_cast<AllocaInst>(I))
-      if (NonInstrumentedStaticAllocaVec.count(AI) > 0)
-        AI->moveBefore(InsBefore);
+  for (auto *AI : StaticAllocasToMoveUp)
+    if (AI->getParent() == InsBeforeB)
+      AI->moveBefore(InsBefore);
 
   // If we have a call to llvm.localescape, keep it in the entry block.
   if (LocalEscapeCall) LocalEscapeCall->moveBefore(InsBefore);