Fix bug so that programIndex (et al.) are available in the debugger.

It's now possible to successfully print out the value of programIndex,
programCount, etc., in the debugger.  The issue was that they were
defined as having InternalLinkage, which meant that DCE removed them
at the end of compilation.  Now they're declared to have WeakODRLinkage,
which ensures that one copy survives (but there aren't multiply-defined
symbols when compiling multiple files.)

builtins.cpp

@@ -637,16 +637,36 @@ AddBitcodeToModule(const unsigned char *bitcode, int length,
 static void
 lDefineConstantInt(const char *name, int val, llvm::Module *module,
                    SymbolTable *symbolTable) {
-    Symbol *pw = 
+    Symbol *sym = 
         new Symbol(name, SourcePos(), AtomicType::UniformInt32->GetAsConstType(),
                    SC_STATIC);
-    pw->constValue = new ConstExpr(pw->type, val, SourcePos());
+    sym->constValue = new ConstExpr(sym->type, val, SourcePos());
     llvm::Type *ltype = LLVMTypes::Int32Type;
     llvm::Constant *linit = LLVMInt32(val);
-    pw->storagePtr = new llvm::GlobalVariable(*module, ltype, true, 
-                                              llvm::GlobalValue::InternalLinkage,
-                                              linit, pw->name.c_str());
-    symbolTable->AddVariable(pw);
+    // Use WeakODRLinkage rather than InternalLinkage so that a definition
+    // survives even if it's not used in the module, so that the symbol is
+    // there in the debugger.
+    sym->storagePtr = new llvm::GlobalVariable(*module, ltype, true, 
+                                               llvm::GlobalValue::WeakODRLinkage,
+                                               linit, name);
+    symbolTable->AddVariable(sym);
+
+    if (m->diBuilder != NULL) {
+        llvm::DIFile file;
+        llvm::DIType diType = sym->type->GetDIType(file);
+        Assert(diType.Verify());
+        // FIXME? DWARF says that this (and programIndex below) should
+        // have the DW_AT_artifical attribute.  It's not clear if this
+        // matters for anything though.
+        llvm::DIGlobalVariable var = 
+            m->diBuilder->createGlobalVariable(name, 
+                                               file,
+                                               0 /* line */,
+                                               diType,
+                                               true /* static */,
+                                               sym->storagePtr);
+        Assert(var.Verify());
+    }
 }
 
 
@@ -672,21 +692,37 @@ lDefineConstantIntFunc(const char *name, int val, llvm::Module *module,
 
 static void
 lDefineProgramIndex(llvm::Module *module, SymbolTable *symbolTable) {
-    Symbol *pidx = 
+    Symbol *sym = 
         new Symbol("programIndex", SourcePos(), 
                    AtomicType::VaryingInt32->GetAsConstType(), SC_STATIC);
 
     int pi[ISPC_MAX_NVEC];
     for (int i = 0; i < g->target.vectorWidth; ++i)
         pi[i] = i;
-    pidx->constValue = new ConstExpr(pidx->type, pi, SourcePos());
+    sym->constValue = new ConstExpr(sym->type, pi, SourcePos());
 
     llvm::Type *ltype = LLVMTypes::Int32VectorType;
     llvm::Constant *linit = LLVMInt32Vector(pi);
-    pidx->storagePtr = new llvm::GlobalVariable(*module, ltype, true, 
-                                                llvm::GlobalValue::InternalLinkage, linit, 
-                                                pidx->name.c_str());
-    symbolTable->AddVariable(pidx);
+    // See comment in lDefineConstantInt() for why WeakODRLinkage is used here
+    sym->storagePtr = new llvm::GlobalVariable(*module, ltype, true, 
+                                               llvm::GlobalValue::WeakODRLinkage,
+                                               linit, 
+                                               sym->name.c_str());
+    symbolTable->AddVariable(sym);
+
+    if (m->diBuilder != NULL) {
+        llvm::DIFile file;
+        llvm::DIType diType = sym->type->GetDIType(file);
+        Assert(diType.Verify());
+        llvm::DIGlobalVariable var =
+            m->diBuilder->createGlobalVariable(sym->name.c_str(), 
+                                               file,
+                                               0 /* line */,
+                                               diType,
+                                               false /* static */,
+                                               sym->storagePtr);
+        Assert(var.Verify());
+    }
 }
 
 

ctx.cpp

@@ -339,29 +339,6 @@ FunctionEmitContext::FunctionEmitContext(Function *func, Symbol *funSym,
 
         /* And start a scope representing the initial function scope */
         StartScope();
-
-        llvm::DIFile file = funcStartPos.GetDIFile();
-        Symbol *programIndexSymbol = m->symbolTable->LookupVariable("programIndex");
-        Assert(programIndexSymbol && programIndexSymbol->storagePtr);
-        llvm::DIGlobalVariable var =
-            m->diBuilder->createGlobalVariable(programIndexSymbol->name, 
-                                               file,
-                                               funcStartPos.first_line,
-                                               programIndexSymbol->type->GetDIType(file),
-                                               true /* static */,
-                                               programIndexSymbol->storagePtr);
-        Assert(var.Verify());
-
-        Symbol *programCountSymbol = m->symbolTable->LookupVariable("programCount");
-        Assert(programCountSymbol);
-        var = 
-            m->diBuilder->createGlobalVariable(programCountSymbol->name, 
-                                               file,
-                                               funcStartPos.first_line,
-                                               programCountSymbol->type->GetDIType(file),
-                                               true /* static */,
-                                               programCountSymbol->storagePtr);
-        Assert(var.Verify());
     }
 }
 

func.cpp

@@ -198,7 +198,7 @@ Function::emitCode(FunctionEmitContext *ctx, llvm::Function *function,
     // value
     maskSymbol->storagePtr = ctx->GetFullMaskPointer();
 
-    // add debugging info for __mask, programIndex, ...
+    // add debugging info for __mask
     maskSymbol->pos = firstStmtPos;
     ctx->EmitVariableDebugInfo(maskSymbol);