[msan] Stop propagating shadow in blacklisted functions.

With this change all values passed through blacklisted functions
become fully initialized. Previous behavior was to initialize all
loads in blacklisted functions, but apply normal shadow propagation
logic for all other operation.

This makes blacklist applicable in a wider range of situations.

It also makes code for blacklisted functions a lot shorter, which
works as yet another workaround for PR17409.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212268 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Instrumentation/MemorySanitizer.cpp

@@ -511,7 +511,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
   // The following flags disable parts of MSan instrumentation based on
   // blacklist contents and command-line options.
   bool InsertChecks;
-  bool LoadShadow;
+  bool PropagateShadow;
   bool PoisonStack;
   bool PoisonUndef;
   bool CheckReturnValue;
@@ -532,7 +532,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     bool SanitizeFunction = F.getAttributes().hasAttribute(
         AttributeSet::FunctionIndex, Attribute::SanitizeMemory);
     InsertChecks = SanitizeFunction;
-    LoadShadow = SanitizeFunction;
+    PropagateShadow = SanitizeFunction;
     PoisonStack = SanitizeFunction && ClPoisonStack;
     PoisonUndef = SanitizeFunction && ClPoisonUndef;
     // FIXME: Consider using SpecialCaseList to specify a list of functions that
@@ -716,13 +716,14 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
 
     // Finalize PHI nodes.
     for (PHINode *PN : ShadowPHINodes) {
+      Value *S = getShadow(PN);
+      if (isa<Constant>(S)) continue;
       PHINode *PNS = cast<PHINode>(getShadow(PN));
       PHINode *PNO = MS.TrackOrigins ? cast<PHINode>(getOrigin(PN)) : nullptr;
       size_t NumValues = PN->getNumIncomingValues();
       for (size_t v = 0; v < NumValues; v++) {
         PNS->addIncoming(getShadow(PN, v), PN->getIncomingBlock(v));
-        if (PNO)
-          PNO->addIncoming(getOrigin(PN, v), PN->getIncomingBlock(v));
+        if (PNO) PNO->addIncoming(getOrigin(PN, v), PN->getIncomingBlock(v));
       }
     }
 
@@ -856,7 +857,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
   /// \brief Set SV to be the shadow value for V.
   void setShadow(Value *V, Value *SV) {
     assert(!ShadowMap.count(V) && "Values may only have one shadow");
-    ShadowMap[V] = SV;
+    ShadowMap[V] = PropagateShadow ? SV : getCleanShadow(V);
   }
 
   /// \brief Set Origin to be the origin value for V.
@@ -908,6 +909,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
   /// This function either returns the value set earlier with setShadow,
   /// or extracts if from ParamTLS (for function arguments).
   Value *getShadow(Value *V) {
+    if (!PropagateShadow) return getCleanShadow(V);
     if (Instruction *I = dyn_cast<Instruction>(V)) {
       // For instructions the shadow is already stored in the map.
       Value *Shadow = ShadowMap[V];
@@ -1075,7 +1077,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     IRBuilder<> IRB(I.getNextNode());
     Type *ShadowTy = getShadowTy(&I);
     Value *Addr = I.getPointerOperand();
-    if (LoadShadow) {
+    if (PropagateShadow) {
       Value *ShadowPtr = getShadowPtr(Addr, ShadowTy, IRB);
       setShadow(&I,
                 IRB.CreateAlignedLoad(ShadowPtr, I.getAlignment(), "_msld"));
@@ -1090,7 +1092,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
       I.setOrdering(addAcquireOrdering(I.getOrdering()));
 
     if (MS.TrackOrigins) {
-      if (LoadShadow) {
+      if (PropagateShadow) {
         unsigned Alignment = std::max(kMinOriginAlignment, I.getAlignment());
         setOrigin(&I,
                   IRB.CreateAlignedLoad(getOriginPtr(Addr, IRB), Alignment));
@@ -1757,7 +1759,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     Value *Addr = I.getArgOperand(0);
 
     Type *ShadowTy = getShadowTy(&I);
-    if (LoadShadow) {
+    if (PropagateShadow) {
       Value *ShadowPtr = getShadowPtr(Addr, ShadowTy, IRB);
       // We don't know the pointer alignment (could be unaligned SSE load!).
       // Have to assume to worst case.
@@ -1770,7 +1772,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
       insertShadowCheck(Addr, &I);
 
     if (MS.TrackOrigins) {
-      if (LoadShadow)
+      if (PropagateShadow)
         setOrigin(&I, IRB.CreateLoad(getOriginPtr(Addr, IRB)));
       else
         setOrigin(&I, getCleanOrigin());

test/Instrumentation/MemorySanitizer/msan_basic.ll

@@ -683,7 +683,7 @@ entry:
 ; CHECK: ret void
 
 
-; Test that checks are omitted but shadow propagation is kept if
+; Test that checks are omitted and returned value is always initialized if
 ; sanitize_memory attribute is missing.
 
 define i32 @NoSanitizeMemory(i32 %x) uwtable {
@@ -703,9 +703,7 @@ declare void @bar()
 
 ; CHECK: @NoSanitizeMemory
 ; CHECK-NOT: @__msan_warning
-; CHECK: load i32* {{.*}} @__msan_param_tls
-; CHECK-NOT: @__msan_warning
-; CHECK: store {{.*}} @__msan_retval_tls
+; CHECK: store i32 0, {{.*}} @__msan_retval_tls
 ; CHECK-NOT: @__msan_warning
 ; CHECK: ret i32
 
@@ -828,7 +826,7 @@ entry:
 
 declare i32 @InnerTailCall(i32 %a)
 
-define void @MismatchedReturnTypeTailCall(i32 %a) {
+define void @MismatchedReturnTypeTailCall(i32 %a) sanitize_memory {
   %b = tail call i32 @InnerTailCall(i32 %a)
   ret void
 }