[CIR] Simlipify string literal global creation (llvm#1632)

Previously, when emitting a global for a string literal, we were
creating a GlobalOp, building a GlobalView attr for it, and looking up
the global from the symbol associated with the attr. This change splits
out the function that creates the global so that the global is returned
directly and the GlobalView attribute is only created in the case where
it is needed.

This also updates the mechanism used for uniquing the global name used
for the strings so that if different base names are used the uniquing
numbers each base name separately. The mangling of the global used for
strings is not implemented, but the uniquing was happening prior to the
mangling. This change drops the uniquing below the placeholder for
mangling.

Author: andykaylor

clang/lib/CIR/CodeGen/CIRGenExpr.cpp

@@ -1880,21 +1880,14 @@ LValue CIRGenFunction::emitArraySubscriptExpr(const ArraySubscriptExpr *E,
   return LV;
 }
 
-LValue CIRGenFunction::emitStringLiteralLValue(const StringLiteral *E) {
-  auto sym = CGM.getAddrOfConstantStringFromLiteral(E).getSymbol();
-
-  auto cstGlobal = mlir::SymbolTable::lookupSymbolIn(CGM.getModule(), sym);
-  assert(cstGlobal && "Expected global");
-
-  auto g = dyn_cast<cir::GlobalOp>(cstGlobal);
-  assert(g && "unaware of other symbol providers");
-
+LValue CIRGenFunction::emitStringLiteralLValue(const StringLiteral *e) {
+  auto g = CGM.getGlobalForStringLiteral(e);
   assert(g.getAlignment() && "expected alignment for string literal");
   auto align = *g.getAlignment();
-  auto addr = builder.createGetGlobal(getLoc(E->getSourceRange()), g);
+  auto addr = builder.createGetGlobal(getLoc(e->getSourceRange()), g);
   return makeAddrLValue(
       Address(addr, g.getSymType(), CharUnits::fromQuantity(align)),
-      E->getType(), AlignmentSource::Decl);
+      e->getType(), AlignmentSource::Decl);
 }
 
 /// Casts are never lvalues unless that cast is to a reference type. If the cast

clang/lib/CIR/CodeGen/CIRGenModule.cpp

@@ -1783,10 +1783,32 @@ generateStringLiteral(mlir::Location loc, mlir::TypedAttr c,
   return gv;
 }
 
-/// Return a pointer to a constant array for the given string literal.
-cir::GlobalViewAttr
-CIRGenModule::getAddrOfConstantStringFromLiteral(const StringLiteral *s,
-                                                 StringRef name) {
+// LLVM IR automatically uniques names when new llvm::GlobalVariables are
+// created. This is handy, for example, when creating globals for string
+// literals. Since we don't do that when creating cir::GlobalOp's, we need
+// a mechanism to generate a unique name in advance.
+//
+// For now, this mechanism is only used in cases where we know that the
+// name is compiler-generated, so we don't use the MLIR symbol table for
+// the lookup.
+std::string CIRGenModule::getUniqueGlobalName(const std::string &baseName) {
+  // If this is the first time we've generated a name for this basename, use
+  // it as is and start a counter for this base name.
+  auto it = cgGlobalNames.find(baseName);
+  if (it == cgGlobalNames.end()) {
+    cgGlobalNames[baseName] = 1;
+    return baseName;
+  }
+
+  std::string result =
+      baseName + "." + std::to_string(cgGlobalNames[baseName]++);
+  // There should not be any symbol with this name in the module.
+  assert(!mlir::SymbolTable::lookupSymbolIn(theModule, result));
+  return result;
+}
+
+cir::GlobalOp CIRGenModule::getGlobalForStringLiteral(const StringLiteral *s,
+                                                      StringRef name) {
   CharUnits alignment =
       astContext.getAlignOfGlobalVarInChars(s->getType(), /*VD=*/nullptr);
 
@@ -1800,13 +1822,6 @@ CIRGenModule::getAddrOfConstantStringFromLiteral(const StringLiteral *s,
         uint64_t(alignment.getQuantity()) > *gv.getAlignment())
       gv.setAlignmentAttr(getSize(alignment));
   } else {
-    SmallString<256> stringNameBuffer = name;
-    llvm::raw_svector_ostream out(stringNameBuffer);
-    if (StringLiteralCnt)
-      out << '.' << StringLiteralCnt;
-    name = out.str();
-    StringLiteralCnt++;
-
     SmallString<256> mangledNameBuffer;
     StringRef globalVariableName;
     auto lt = cir::GlobalLinkageKind::ExternalLinkage;
@@ -1822,18 +1837,28 @@ CIRGenModule::getAddrOfConstantStringFromLiteral(const StringLiteral *s,
       globalVariableName = name;
     }
 
+    // Unlike LLVM IR, CIR doesn't automatically unique names for globals, so
+    // we need to do that explicitly.
+    std::string uniqueName = getUniqueGlobalName(globalVariableName.str());
     auto loc = getLoc(s->getSourceRange());
     auto typedC = llvm::dyn_cast<mlir::TypedAttr>(c);
     if (!typedC)
       llvm_unreachable("this should never be untyped at this point");
-    gv = generateStringLiteral(loc, typedC, lt, *this, globalVariableName,
-                               alignment);
+    gv = generateStringLiteral(loc, typedC, lt, *this, uniqueName, alignment);
     setDSOLocal(static_cast<mlir::Operation *>(gv));
     ConstantStringMap[c] = gv;
 
     assert(!cir::MissingFeatures::reportGlobalToASan() && "NYI");
   }
 
+  return gv;
+}
+
+/// Return a pointer to a constant array for the given string literal.
+cir::GlobalViewAttr
+CIRGenModule::getAddrOfConstantStringFromLiteral(const StringLiteral *s,
+                                                 StringRef name) {
+  auto gv = getGlobalForStringLiteral(s, name);
   auto arrayTy = mlir::dyn_cast<cir::ArrayType>(gv.getSymType());
   assert(arrayTy && "String literal must be array");
   auto ptrTy = getBuilder().getPointerTo(arrayTy.getElementType(),

clang/lib/CIR/CodeGen/CIRGenModule.h

@@ -338,6 +338,9 @@ class CIRGenModule : public CIRGenTypeCache {
     return !getLangOpts().CPlusPlus;
   }
 
+  llvm::StringMap<unsigned> cgGlobalNames;
+  std::string getUniqueGlobalName(const std::string &baseName);
+
   /// Return the mlir::Value for the address of the given global variable.
   /// If Ty is non-null and if the global doesn't exist, then it will be created
   /// with the specified type instead of whatever the normal requested type
@@ -444,12 +447,15 @@ class CIRGenModule : public CIRGenTypeCache {
   /// Return a constant array for the given string.
   mlir::Attribute getConstantArrayFromStringLiteral(const StringLiteral *E);
 
+  /// Return a global op for the given string literal.
+  cir::GlobalOp getGlobalForStringLiteral(const StringLiteral *s,
+                                          llvm::StringRef name = ".str");
+
   /// Return a global symbol reference to a constant array for the given string
   /// literal.
   cir::GlobalViewAttr
   getAddrOfConstantStringFromLiteral(const StringLiteral *S,
                                      llvm::StringRef Name = ".str");
-  unsigned StringLiteralCnt = 0;
 
   unsigned CompoundLitaralCnt = 0;
   /// Return the unique name for global compound literal