Fix IRInterpreter guard variable replacement.

[zturner]

Summary

MS ABI guard variables end with @4IA, so this patch teaches the interpreter about that. Additionally, there was an issue with TurnGuardLoadIntoZero which was causing some guard uses of a variable to be missed. This fixes that by calling Instruction::replaceAllUsesWith() instead of trying to replicate that function.

This fixes between 8 and 10 tests on Windows, and in particular fixes evaluation of C / C++ local variables.

[zturner]

+Sean Callanan <[e-mail]>​

I couldn't include you on the Phabricator issue Sean, so I'm CC'ing you
directly. PTAL

source/Expression/IRForTarget.cpp

 
     GlobalVariable *GV = dyn_cast<GlobalVariable>(Old);
 
-    if (!GV || !GV->hasName() || !GV->getName().startswith("_ZGV"))
+    if (!GV || !GV->hasName() ||
+        (!GV->getName().startswith("_ZGV") && // Itanium ABI guard variable
+         !GV->getName().endswith("@4IA")))    // Microsoft ABI guard variable
+    {
         return false;
+    }
 
     return true;
 }

 void
 IRForTarget::TurnGuardLoadIntoZero(llvm::Instruction* guard_load)
 {
-    Constant* zero(ConstantInt::get(Type::getInt8Ty(m_module->getContext()), 0, true));
-
-    for (llvm::User *u : guard_load->users())
-    {
-        if (isa<Constant>(u))
-        {
-            // do nothing for the moment
-        }
-        else
-        {
-            u->replaceUsesOfWith(guard_load, zero);
-        }
-    }
-
+    Constant *zero(Constant::getNullValue(guard_load->getType()));
+    guard_load->replaceAllUsesWith(zero);
     guard_load->eraseFromParent();
 }