From d9434ef62ffbc1ba4c16437b899f7ceeb63dfa03 Mon Sep 17 00:00:00 2001
From: Evgeniy Stepanov <eugeni.stepanov@gmail.com>
Date: Tue, 20 Jan 2015 15:21:35 +0000
Subject: [PATCH] [msan] Optimize -msan-check-constant-shadow.

The new code does not create new basic blocks in the case when shadow is a
compile-time constant; it generates either an unconditional __msan_warning
call or nothing instead.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226569 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../Instrumentation/MemorySanitizer.cpp       | 34 ++++++++++++----
 .../MemorySanitizer/check-constant-shadow.ll  | 40 ++++++++++++++++++-
 2 files changed, 65 insertions(+), 9 deletions(-)

diff --git a/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index 34f49fb7c10..d97eb31962a 100644
--- a/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -611,11 +611,15 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
                              OriginAlignment);
     } else {
       Value *ConvertedShadow = convertToShadowTyNoVec(Shadow, IRB);
-      // TODO(eugenis): handle non-zero constant shadow by inserting an
-      // unconditional check (can not simply fail compilation as this could
-      // be in the dead code).
-      if (!ClCheckConstantShadow)
-        if (isa<Constant>(ConvertedShadow)) return;
+      Constant *ConstantShadow = dyn_cast_or_null<Constant>(ConvertedShadow);
+      if (ConstantShadow) {
+        if (ClCheckConstantShadow && !ConstantShadow->isZeroValue())
+          IRB.CreateAlignedStore(updateOrigin(Origin, IRB),
+                                 getOriginPtr(Addr, IRB, Alignment),
+                                 OriginAlignment);
+        return;
+      }
+
       unsigned TypeSizeInBits =
           MS.DL->getTypeSizeInBits(ConvertedShadow->getType());
       unsigned SizeIndex = TypeSizeToSizeIndex(TypeSizeInBits);
@@ -670,9 +674,23 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     DEBUG(dbgs() << "  SHAD0 : " << *Shadow << "\n");
     Value *ConvertedShadow = convertToShadowTyNoVec(Shadow, IRB);
     DEBUG(dbgs() << "  SHAD1 : " << *ConvertedShadow << "\n");
-    // See the comment in storeOrigin().
-    if (!ClCheckConstantShadow)
-      if (isa<Constant>(ConvertedShadow)) return;
+
+    Constant *ConstantShadow = dyn_cast_or_null<Constant>(ConvertedShadow);
+    if (ConstantShadow) {
+      if (ClCheckConstantShadow && !ConstantShadow->isZeroValue()) {
+        if (MS.TrackOrigins) {
+          IRB.CreateStore(Origin ? (Value *)Origin : (Value *)IRB.getInt32(0),
+                          MS.OriginTLS);
+        }
+        IRB.CreateCall(MS.WarningFn);
+        IRB.CreateCall(MS.EmptyAsm);
+        // FIXME: Insert UnreachableInst if !ClKeepGoing?
+        // This may invalidate some of the following checks and needs to be done
+        // at the very end.
+      }
+      return;
+    }
+
     unsigned TypeSizeInBits =
         MS.DL->getTypeSizeInBits(ConvertedShadow->getType());
     unsigned SizeIndex = TypeSizeToSizeIndex(TypeSizeInBits);
diff --git a/test/Instrumentation/MemorySanitizer/check-constant-shadow.ll b/test/Instrumentation/MemorySanitizer/check-constant-shadow.ll
index 11e44106d8f..f1479440faf 100644
--- a/test/Instrumentation/MemorySanitizer/check-constant-shadow.ll
+++ b/test/Instrumentation/MemorySanitizer/check-constant-shadow.ll
@@ -1,10 +1,11 @@
-; RUN: opt < %s -msan -msan-check-constant-shadow=1 -S | FileCheck %s
+; RUN: opt < %s -msan -msan-check-access-address=0 -msan-check-constant-shadow=1 -msan-track-origins=1 -S | FileCheck %s
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 ; Test that returning a literal undef from main() triggers an MSan warning.
 
+; main() is special: it inserts check for the return value
 define i32 @main() nounwind uwtable sanitize_memory {
 entry:
   ret i32 undef
@@ -13,3 +14,40 @@ entry:
 ; CHECK-LABEL: @main
 ; CHECK: call void @__msan_warning_noreturn
 ; CHECK: ret i32 undef
+
+
+; This function stores known initialized value.
+; Expect 2 stores: one for the shadow (0), one for the value (42), but no origin.
+define void @StoreConstant(i32* nocapture %p) nounwind uwtable sanitize_memory {
+entry:
+  store i32 42, i32* %p, align 4
+  ret void
+}
+
+; CHECK-LABEL: @StoreConstant
+; CHECK-NOT: store i32
+; CHECK: store i32 0,
+; CHECK-NOT: store i32
+; CHECK: store i32 42,
+; CHECK-NOT: store i32
+; CHECK: ret void
+
+
+; This function stores known uninitialized value.
+; Expect 3 stores: shadow, value and origin.
+; Expect no icmp(s): everything here is unconditional.
+define void @StoreUndef(i32* nocapture %p) nounwind uwtable sanitize_memory {
+entry:
+  store i32 undef, i32* %p, align 4
+  ret void
+}
+
+; CHECK-LABEL: @StoreUndef
+; CHECK-NOT: icmp
+; CHECK: store i32
+; CHECK-NOT: icmp
+; CHECK: store i32
+; CHECK-NOT: icmp
+; CHECK: store i32
+; CHECK-NOT: icmp
+; CHECK: ret void
-- 
2.34.1