- Re-apply 52748 and friends with fix. GetConstantStringInfo() returns an empty string for ConstantAggregateZero case which surprises selectiondag.

- Correctly handle memcpy from constant string which is zero-initialized.

llvm-svn: 52891

llvm/lib/CodeGen/MachineModuleInfo.cpp

@@ -10,6 +10,7 @@
 #include "llvm/CodeGen/MachineModuleInfo.h"
 
 #include "llvm/Constants.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineLocation.h"
@@ -206,7 +207,9 @@ public:
   }
   virtual void Apply(std::string &Field) {
     Constant *C = CI->getOperand(I++);
-    Field = C->getStringValue();
+    // Fills in the string if it succeeds
+    if (!GetConstantStringInfo(C, Field))
+      Field.clear();
   }
   virtual void Apply(DebugInfoDesc *&Field) {
     Constant *C = CI->getOperand(I++);