From 42a9da35b839b3a2bb0c891ecc7e138da016f1dd Mon Sep 17 00:00:00 2001
From: Kostya Serebryany <kcc@google.com>
Date: Thu, 21 Nov 2013 07:29:28 +0000
Subject: [PATCH] Don't speculate loads under ThreadSanitizer

Summary:
Don't speculate loads under ThreadSanitizer.
This fixes https://code.google.com/p/thread-sanitizer/issues/detail?id=40
Also discussed here: http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-November/067929.html

Reviewers: chandlerc

Reviewed By: chandlerc

CC: llvm-commits, dvyukov

Differential Revision: http://llvm-reviews.chandlerc.com/D2227

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195324 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ValueTracking.cpp                |  4 +-
 .../no_speculative_loads_with_tsan.ll         | 40 +++++++++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)
 create mode 100644 test/Transforms/SimplifyCFG/no_speculative_loads_with_tsan.ll

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index e39ee628ff0..803051d0bb2 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -2006,7 +2006,9 @@ bool llvm::isSafeToSpeculativelyExecute(const Value *V,
   }
   case Instruction::Load: {
     const LoadInst *LI = cast<LoadInst>(Inst);
-    if (!LI->isUnordered())
+    if (!LI->isUnordered() ||
+        // Speculative load may create a race that did not exist in the source.
+        LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeThread))
       return false;
     return LI->getPointerOperand()->isDereferenceablePointer();
   }
diff --git a/test/Transforms/SimplifyCFG/no_speculative_loads_with_tsan.ll b/test/Transforms/SimplifyCFG/no_speculative_loads_with_tsan.ll
new file mode 100644
index 00000000000..b388cc5830f
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/no_speculative_loads_with_tsan.ll
@@ -0,0 +1,40 @@
+; RUN: opt -simplifycfg -S %s | FileCheck %s
+; Make sure we don't speculate loads under ThreadSanitizer.
+@g = global i32 0, align 4
+
+define i32 @TestNoTsan(i32 %cond) nounwind readonly uwtable {
+entry:
+  %tobool = icmp eq i32 %cond, 0
+  br i1 %tobool, label %return, label %if.then
+
+if.then:                                          ; preds = %entry
+  %0 = load i32* @g, align 4
+  br label %return
+
+return:                                           ; preds = %entry, %if.then
+  %retval = phi i32 [ %0, %if.then ], [ 0, %entry ]
+  ret i32 %retval
+; CHECK-LABEL: @TestNoTsan
+; CHECK: %[[LOAD:[^ ]*]] = load
+; CHECK: select{{.*}}[[LOAD]]
+; CHECK: ret i32
+}
+
+define i32 @TestTsan(i32 %cond) nounwind readonly uwtable sanitize_thread {
+entry:
+  %tobool = icmp eq i32 %cond, 0
+  br i1 %tobool, label %return, label %if.then
+
+if.then:                                          ; preds = %entry
+  %0 = load i32* @g, align 4
+  br label %return
+
+return:                                           ; preds = %entry, %if.then
+  %retval = phi i32 [ %0, %if.then ], [ 0, %entry ]
+  ret i32 %retval
+; CHECK-LABEL: @TestTsan
+; CHECK: br i1
+; CHECK: load i32* @g
+; CHECK: br label
+; CHECK: ret i32
+}