[CIR][CIRGen] Add initial CIRGen support for local temporary materialization (llvm#820)

This PR adds initial support for temporary materialization of local
temporaries with trivial cleanups.

Materialization of global temporaries and local temporaries with
non-trivial cleanups is far more trickier that I initially thought and I
decide to submit this easy part first.

Author: Lancern

clang/lib/CIR/CodeGen/CIRGenExpr.cpp

@@ -2146,8 +2146,22 @@ static Address createReferenceTemporary(CIRGenFunction &CGF,
         (Ty->isArrayType() || Ty->isRecordType()) &&
         CGF.CGM.isTypeConstant(Ty, /*ExcludeCtor=*/true, /*ExcludeDtor=*/false))
       assert(0 && "NYI");
+
+    // The temporary memory should be created in the same scope as the extending
+    // declaration of the temporary materialization expression.
+    mlir::cir::AllocaOp extDeclAlloca;
+    if (const clang::ValueDecl *extDecl = M->getExtendingDecl()) {
+      auto extDeclAddrIter = CGF.LocalDeclMap.find(extDecl);
+      if (extDeclAddrIter != CGF.LocalDeclMap.end()) {
+        extDeclAlloca = dyn_cast_if_present<mlir::cir::AllocaOp>(
+            extDeclAddrIter->second.getDefiningOp());
+      }
+    }
+    mlir::OpBuilder::InsertPoint ip;
+    if (extDeclAlloca)
+      ip = {extDeclAlloca->getBlock(), extDeclAlloca->getIterator()};
     return CGF.CreateMemTemp(Ty, CGF.getLoc(M->getSourceRange()),
-                             CGF.getCounterRefTmpAsString(), Alloca);
+                             CGF.getCounterRefTmpAsString(), Alloca, ip);
   }
   case SD_Thread:
   case SD_Static:
@@ -2245,7 +2259,7 @@ LValue CIRGenFunction::buildMaterializeTemporaryExpr(
   } else {
     switch (M->getStorageDuration()) {
     case SD_Automatic:
-      assert(0 && "NYI");
+      assert(!MissingFeatures::shouldEmitLifetimeMarkers());
       break;
 
     case SD_FullExpression: {
@@ -2932,18 +2946,20 @@ void CIRGenFunction::buildUnreachable(SourceLocation Loc) {
 //===----------------------------------------------------------------------===//
 
 Address CIRGenFunction::CreateMemTemp(QualType Ty, mlir::Location Loc,
-                                      const Twine &Name, Address *Alloca) {
+                                      const Twine &Name, Address *Alloca,
+                                      mlir::OpBuilder::InsertPoint ip) {
   // FIXME: Should we prefer the preferred type alignment here?
   return CreateMemTemp(Ty, getContext().getTypeAlignInChars(Ty), Loc, Name,
-                       Alloca);
+                       Alloca, ip);
 }
 
 Address CIRGenFunction::CreateMemTemp(QualType Ty, CharUnits Align,
                                       mlir::Location Loc, const Twine &Name,
-                                      Address *Alloca) {
+                                      Address *Alloca,
+                                      mlir::OpBuilder::InsertPoint ip) {
   Address Result =
       CreateTempAlloca(getTypes().convertTypeForMem(Ty), Align, Loc, Name,
-                       /*ArraySize=*/nullptr, Alloca);
+                       /*ArraySize=*/nullptr, Alloca, ip);
   if (Ty->isConstantMatrixType()) {
     assert(0 && "NYI");
   }

clang/lib/CIR/CodeGen/CIRGenFunction.h

@@ -2215,9 +2215,11 @@ class CIRGenFunction : public CIRGenTypeCache {
   /// appropriate alignmen and cast it to the default address space. Returns
   /// the original alloca instruction by \p Alloca if it is not nullptr.
   Address CreateMemTemp(QualType T, mlir::Location Loc,
-                        const Twine &Name = "tmp", Address *Alloca = nullptr);
+                        const Twine &Name = "tmp", Address *Alloca = nullptr,
+                        mlir::OpBuilder::InsertPoint ip = {});
   Address CreateMemTemp(QualType T, CharUnits Align, mlir::Location Loc,
-                        const Twine &Name = "tmp", Address *Alloca = nullptr);
+                        const Twine &Name = "tmp", Address *Alloca = nullptr,
+                        mlir::OpBuilder::InsertPoint ip = {});
 
   /// Create a temporary memory object of the given type, with
   /// appropriate alignment without casting it to the default address space.

clang/test/CIR/CodeGen/temporary-materialization.cpp

@@ -0,0 +1,43 @@
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s
+
+int make_int();
+
+int test() {
+  const int &x = make_int();
+  return x;
+}
+
+//      CHECK: cir.func @_Z4testv()
+// CHECK-NEXT:   %{{.+}} = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"] {alignment = 4 : i64}
+// CHECK-NEXT:   %[[#TEMP_SLOT:]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["ref.tmp0", init] {alignment = 4 : i64}
+// CHECK-NEXT:   %[[#x:]] = cir.alloca !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>, ["x", init] {alignment = 8 : i64}
+// CHECK-NEXT:   cir.scope {
+// CHECK-NEXT:     %[[#TEMP_VALUE:]] = cir.call @_Z8make_intv() : () -> !s32i
+// CHECK-NEXT:     cir.store %[[#TEMP_VALUE]], %[[#TEMP_SLOT]] : !s32i, !cir.ptr<!s32i>
+// CHECK-NEXT:   }
+// CHECK-NEXT:   cir.store %[[#TEMP_SLOT]], %[[#x]] : !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>
+//      CHECK: }
+
+int test_scoped() {
+  int x = make_int();
+  {
+    const int &y = make_int();
+    x = y;
+  }
+  return x;
+}
+
+//      CHECK: cir.func @_Z11test_scopedv()
+// CHECK-NEXT:   %{{.+}} = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"] {alignment = 4 : i64}
+// CHECK-NEXT:   %{{.+}} = cir.alloca !s32i, !cir.ptr<!s32i>, ["x", init] {alignment = 4 : i64}
+//      CHECK:   cir.scope {
+// CHECK-NEXT:     %[[#TEMP_SLOT:]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["ref.tmp0", init] {alignment = 4 : i64}
+// CHECK-NEXT:     %[[#y:]] = cir.alloca !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>, ["y", init] {alignment = 8 : i64}
+// CHECK-NEXT:     cir.scope {
+// CHECK-NEXT:       %[[#TEMP_VALUE:]] = cir.call @_Z8make_intv() : () -> !s32i
+// CHECK-NEXT:       cir.store %[[#TEMP_VALUE]], %[[#TEMP_SLOT]] : !s32i, !cir.ptr<!s32i>
+// CHECK-NEXT:     }
+// CHECK-NEXT:     cir.store %[[#TEMP_SLOT]], %[[#y]] : !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>
+//      CHECK:   }
+//      CHECK: }