[MSan] Introduce ActualFnStart. NFC

This is a step towards the upcoming KMSAN implementation patch.
KMSAN is going to prepend a special basic block containing
tool-specific calls to each function. Because we still want to
instrument the original entry block, we'll need to store it in
ActualFnStart.

For MSan this will still be F.getEntryBlock(), whereas for KMSAN
it'll contain the second BB.

llvm-svn: 328697

llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

@@ -715,6 +715,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
   ValueMap<Value*, Value*> ShadowMap, OriginMap;
   std::unique_ptr<VarArgHelper> VAHelper;
   const TargetLibraryInfo *TLI;
+  BasicBlock *ActualFnStart;
 
   // The following flags disable parts of MSan instrumentation based on
   // blacklist contents and command-line options.
@@ -747,6 +748,9 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     CheckReturnValue = SanitizeFunction && (F.getName() == "main");
     TLI = &MS.getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
 
+    MS.initializeCallbacks(*F.getParent());
+    ActualFnStart = &F.getEntryBlock();
+
     DEBUG(if (!InsertChecks)
           dbgs() << "MemorySanitizer is not inserting checks into '"
                  << F.getName() << "'\n");
@@ -931,8 +935,6 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
 
   /// \brief Add MemorySanitizer instrumentation to a function.
   bool runOnFunction() {
-    MS.initializeCallbacks(*F.getParent());
-
     // In the presence of unreachable blocks, we may see Phi nodes with
     // incoming nodes from such blocks. Since InstVisitor skips unreachable
     // blocks, such nodes will not have any shadow value associated with them.
@@ -942,7 +944,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     // Iterate all BBs in depth-first order and create shadow instructions
     // for all instructions (where applicable).
     // For PHI nodes we create dummy shadow PHIs which will be finalized later.
-    for (BasicBlock *BB : depth_first(&F.getEntryBlock()))
+    for (BasicBlock *BB : depth_first(ActualFnStart))
       visit(*BB);
 
     // Finalize PHI nodes.
@@ -1216,7 +1218,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
       if (*ShadowPtr)
         return *ShadowPtr;
       Function *F = A->getParent();
-      IRBuilder<> EntryIRB(F->getEntryBlock().getFirstNonPHI());
+      IRBuilder<> EntryIRB(ActualFnStart->getFirstNonPHI());
       unsigned ArgOffset = 0;
       const DataLayout &DL = F->getParent()->getDataLayout();
       for (auto &FArg : F->args()) {
@@ -3214,7 +3216,7 @@ struct VarArgAMD64Helper : public VarArgHelper {
     if (!VAStartInstrumentationList.empty()) {
       // If there is a va_start in this function, make a backup copy of
       // va_arg_tls somewhere in the function entry block.
-      IRBuilder<> IRB(F.getEntryBlock().getFirstNonPHI());
+      IRBuilder<> IRB(MSV.ActualFnStart->getFirstNonPHI());
       VAArgOverflowSize = IRB.CreateLoad(MS.VAArgOverflowSizeTLS);
       Value *CopySize =
         IRB.CreateAdd(ConstantInt::get(MS.IntptrTy, AMD64FpEndOffset),
@@ -3336,7 +3338,7 @@ struct VarArgMIPS64Helper : public VarArgHelper {
   void finalizeInstrumentation() override {
     assert(!VAArgSize && !VAArgTLSCopy &&
            "finalizeInstrumentation called twice");
-    IRBuilder<> IRB(F.getEntryBlock().getFirstNonPHI());
+    IRBuilder<> IRB(MSV.ActualFnStart->getFirstNonPHI());
     VAArgSize = IRB.CreateLoad(MS.VAArgOverflowSizeTLS);
     Value *CopySize = IRB.CreateAdd(ConstantInt::get(MS.IntptrTy, 0),
                                     VAArgSize);
@@ -3521,7 +3523,7 @@ struct VarArgAArch64Helper : public VarArgHelper {
     if (!VAStartInstrumentationList.empty()) {
       // If there is a va_start in this function, make a backup copy of
       // va_arg_tls somewhere in the function entry block.
-      IRBuilder<> IRB(F.getEntryBlock().getFirstNonPHI());
+      IRBuilder<> IRB(MSV.ActualFnStart->getFirstNonPHI());
       VAArgOverflowSize = IRB.CreateLoad(MS.VAArgOverflowSizeTLS);
       Value *CopySize =
         IRB.CreateAdd(ConstantInt::get(MS.IntptrTy, AArch64VAEndOffset),
@@ -3757,7 +3759,7 @@ struct VarArgPowerPC64Helper : public VarArgHelper {
   void finalizeInstrumentation() override {
     assert(!VAArgSize && !VAArgTLSCopy &&
            "finalizeInstrumentation called twice");
-    IRBuilder<> IRB(F.getEntryBlock().getFirstNonPHI());
+    IRBuilder<> IRB(MSV.ActualFnStart->getFirstNonPHI());
     VAArgSize = IRB.CreateLoad(MS.VAArgOverflowSizeTLS);
     Value *CopySize = IRB.CreateAdd(ConstantInt::get(MS.IntptrTy, 0),
                                     VAArgSize);