From f0500b6ae526fef8238f4f6017ac9da2f5c3f756 Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka@google.com>
Date: Thu, 28 Jul 2016 22:50:48 +0000
Subject: [PATCH] Do not remove empty lifetime.start/lifetime.end ranges

Summary:
Asan stack-use-after-scope check should poison alloca even if there is
no access between start and end.

This is possible for code like this:
for (int i = 0; i < 3; i++) {
  int x;
  p = &x;
}

"Loop Invariant Code Motion" will move "p = &x;" out of the loop, making
start/end range empty.

PR27453

Reviewers: eugenis

Differential Revision: https://reviews.llvm.org/D22842

llvm-svn: 277068
---
 llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp | 13 +++++--------
 llvm/test/Transforms/InstCombine/lifetime-asan.ll    | 18 ++++++++----------
 2 files changed, 13 insertions(+), 18 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 5446ce0..52c3777 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -30,8 +30,6 @@ using namespace PatternMatch;
 
 STATISTIC(NumSimplified, "Number of library calls simplified");
 
-extern cl::opt<bool> ClUseAfterScope;
-
 /// Return the specified type promoted as it would be to pass though a va_arg
 /// area.
 static Type *getPromotedType(Type *Ty) {
@@ -2244,18 +2242,16 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
       return eraseInstFromFunction(CI);
     break;
   }
-  case Intrinsic::lifetime_start: {
-    const Function *func = II->getFunction();
-    // Asan needs to poison memory to detect invalid access possible even for
-    // empty lifetime range.
-    if (func && func->hasFnAttribute(Attribute::SanitizeAddress))
+  case Intrinsic::lifetime_start:
+    // Asan needs to poison memory to detect invalid access which is possible
+    // even for empty lifetime range.
+    if (II->getFunction()->hasFnAttribute(Attribute::SanitizeAddress))
       break;
 
     if (removeTriviallyEmptyRange(*II, Intrinsic::lifetime_start,
                                   Intrinsic::lifetime_end, *this))
       return nullptr;
     break;
-  }
   case Intrinsic::assume: {
     Value *IIOperand = II->getArgOperand(0);
     // Remove an assume if it is immediately followed by an identical assume.
@@ -2486,6 +2482,7 @@ static IntrinsicInst *findInitTrampoline(Value *Callee) {
 
 /// Improvements for call and invoke instructions.
 Instruction *InstCombiner::visitCallSite(CallSite CS) {
+
   if (isAllocLikeFn(CS.getInstruction(), TLI))
     return visitAllocSite(*CS.getInstruction());
 
diff --git a/llvm/test/Transforms/InstCombine/lifetime-asan.ll b/llvm/test/Transforms/InstCombine/lifetime-asan.ll
index fc55197..f52c020 100644
--- a/llvm/test/Transforms/InstCombine/lifetime-asan.ll
+++ b/llvm/test/Transforms/InstCombine/lifetime-asan.ll
@@ -7,15 +7,14 @@ declare void @foo(i8* nocapture)
 define void @asan() sanitize_address {
 entry:
   ; CHECK-LABEL: @asan(
-  %text = alloca [1 x i8], align 1
-  %0 = getelementptr inbounds [1 x i8], [1 x i8]* %text, i64 0, i64 0
+  %text = alloca i8, align 1
 
-  call void @llvm.lifetime.start(i64 1, i8* %0)
-  call void @llvm.lifetime.end(i64 1, i8* %0)
+  call void @llvm.lifetime.start(i64 1, i8* %text)
+  call void @llvm.lifetime.end(i64 1, i8* %text)
   ; CHECK: call void @llvm.lifetime.start
   ; CHECK-NEXT: call void @llvm.lifetime.end
 
-  call void @foo(i8* %0) ; Keep alloca alive
+  call void @foo(i8* %text) ; Keep alloca alive
 
   ret void
 }
@@ -24,14 +23,13 @@ entry:
 define void @no_asan() {
 entry:
   ; CHECK-LABEL: @no_asan(
-  %text = alloca [1 x i8], align 1
-  %0 = getelementptr inbounds [1 x i8], [1 x i8]* %text, i64 0, i64 0
+  %text = alloca i8, align 1
 
-  call void @llvm.lifetime.start(i64 1, i8* %0)
-  call void @llvm.lifetime.end(i64 1, i8* %0)
+  call void @llvm.lifetime.start(i64 1, i8* %text)
+  call void @llvm.lifetime.end(i64 1, i8* %text)
   ; CHECK-NO: call void @llvm.lifetime
 
-  call void @foo(i8* %0) ; Keep alloca alive
+  call void @foo(i8* %text) ; Keep alloca alive
 
   ret void
 }
-- 
2.7.4