[PATCH] D57205: hwasan: If we split the entry block, move static allocas back into the entry block.

[Peter Collingbourne via Phabricator via llvm-commits]

pcc created this revision.
pcc added a reviewer: eugenis.
Herald added a subscriber: hiraditya.

Otherwise they are treated as dynamic allocas, which ends up increasing
code size significantly. This reduces size of Chromium base_unittests
by 2MB (6.7%).


Repository:
  rL LLVM

https://reviews.llvm.org/D57205

Files:
  llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
  llvm/test/Instrumentation/HWAddressSanitizer/lazy-thread-init.ll


Index: llvm/test/Instrumentation/HWAddressSanitizer/lazy-thread-init.ll
===================================================================
--- llvm/test/Instrumentation/HWAddressSanitizer/lazy-thread-init.ll
+++ llvm/test/Instrumentation/HWAddressSanitizer/lazy-thread-init.ll
@@ -2,9 +2,10 @@
 
 target triple = "aarch64--linux-android"
 
-declare void @bar([16 x i32]* %p)
+declare i32 @bar([16 x i32]* %p)
 
 define void @alloca() sanitize_hwaddress "hwasan-abi"="interceptor" {
+  ; CHECK: alloca [16 x i32]
   ; CHECK: [[A:%[^ ]*]] = call i8* @llvm.thread.pointer()
   ; CHECK: [[B:%[^ ]*]] = getelementptr i8, i8* [[A]], i32 48
   ; CHECK: [[C:%[^ ]*]] = bitcast i8* [[B]] to i64*
@@ -19,9 +20,11 @@
 
   ; CHECK: [[CONT]]:
   ; CHECK: phi i64 [ [[LOAD]], %0 ], [ [[RELOAD]], %[[INIT]] ]
+  ; CHECK: alloca i8
 
   %p = alloca [16 x i32]
-  call void @bar([16 x i32]* %p)
+  %size = call i32 @bar([16 x i32]* %p)
+  %q = alloca i8, i32 %size
   ret void
 }
 
Index: llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
+++ llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
@@ -1038,6 +1038,21 @@
     Changed |= instrumentStack(AllocasToInstrument, RetVec, StackTag);
   }
 
+  // If we split the entry block, move any allocas that were originally in the
+  // entry block back into the entry block so that they aren't treated as
+  // dynamic allocas.
+  if (EntryIRB.GetInsertBlock() != &F.getEntryBlock()) {
+    InsertPt = &*F.getEntryBlock().begin();
+    for (auto II = EntryIRB.GetInsertBlock()->begin(),
+              IE = EntryIRB.GetInsertBlock()->end();
+         II != IE;) {
+      Instruction *I = &*II++;
+      if (auto *AI = dyn_cast<AllocaInst>(I))
+        if (isa<ConstantInt>(AI->getArraySize()))
+          I->moveBefore(InsertPt);
+    }
+  }
+
   for (auto Inst : ToInstrument)
     Changed |= instrumentMemAccess(Inst);
 


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