hwasan: If we split the entry block, move static allocas back into the entry block.

[pcc]

Summary

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%).

[eugenis]

LGTM

llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp

bool HWAddressSanitizer::runOnFunction(Function &F) {
 
   bool Changed = false;
   if (!AllocasToInstrument.empty()) {
     Value *StackTag =
         ClGenerateTagsWithCalls ? nullptr : getStackBaseTag(EntryIRB);
     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);
 
   LocalDynamicShadow = nullptr;
 
   return Changed;
 }
 

llvm/test/Instrumentation/HWAddressSanitizer/lazy-thread-init.ll

 ; RUN: opt -S -hwasan -hwasan-allow-ifunc < %s | FileCheck %s
 
 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*
   ; CHECK: [[LOAD:%[^ ]*]] = load i64, i64* [[C]]
   ; CHECK: [[ICMP:%[^ ]*]] = icmp eq i64 [[LOAD]], 0
   ; CHECK: br i1 [[ICMP]], label %[[INIT:[^,]*]], label %[[CONT:[^,]*]], !prof [[PROF:![0-9]+]]
 
   ; CHECK: [[INIT]]:
   ; CHECK: call void @__hwasan_thread_enter()
   ; CHECK: [[RELOAD:%[^ ]*]] = load i64, i64* [[C]]
   ; CHECK: br label %[[CONT]]
 
   ; 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
 }
 
 define i32 @load(i32* %p) sanitize_hwaddress "hwasan-abi"="interceptor" {
   ; CHECK: [[SHADOW:%[^ ]*]] = call i8* asm "", "=r,0"([0 x i8]* @__hwasan_shadow)
   ; CHECK-NOT: icmp
   ; CHECK: call void @llvm.hwasan.check.memaccess(i8* [[SHADOW]],
   %v = load i32, i32* %p
   ret i32 %v
 }
 
 ; CHECK: [[PROF]] = !{!"branch_weights", i32 1, i32 100000}