[clang] [CIR] Upstream support for variable length arrays (PR #163297)

[Amr Hesham via cfe-commits]

================
@@ -44,38 +44,70 @@ CIRGenFunction::emitAutoVarAlloca(const VarDecl &d,
 
   // If the type is variably-modified, emit all the VLA sizes for it.
   if (ty->isVariablyModifiedType())
-    cgm.errorNYI(d.getSourceRange(), "emitAutoVarDecl: variably modified type");
+    emitVariablyModifiedType(ty);
 
   assert(!cir::MissingFeatures::openMP());
 
   Address address = Address::invalid();
-  if (!ty->isConstantSizeType())
-    cgm.errorNYI(d.getSourceRange(), "emitAutoVarDecl: non-constant size type");
-
-  // A normal fixed sized variable becomes an alloca in the entry block,
-  // unless:
-  // - it's an NRVO variable.
-  // - we are compiling OpenMP and it's an OpenMP local variable.
-  if (nrvo) {
-    // The named return value optimization: allocate this variable in the
-    // return slot, so that we can elide the copy when returning this
-    // variable (C++0x [class.copy]p34).
-    address = returnValue;
-
-    if (const RecordDecl *rd = ty->getAsRecordDecl()) {
-      if (const auto *cxxrd = dyn_cast<CXXRecordDecl>(rd);
-          (cxxrd && !cxxrd->hasTrivialDestructor()) ||
-          rd->isNonTrivialToPrimitiveDestroy())
-        cgm.errorNYI(d.getSourceRange(), "emitAutoVarAlloca: set NRVO flag");
+  if (ty->isConstantSizeType()) {
+    // A normal fixed sized variable becomes an alloca in the entry block,
+    // unless:
+    // - it's an NRVO variable.
+    // - we are compiling OpenMP and it's an OpenMP local variable.
+    if (nrvo) {
+      // The named return value optimization: allocate this variable in the
+      // return slot, so that we can elide the copy when returning this
+      // variable (C++0x [class.copy]p34).
+      address = returnValue;
+
+      if (const RecordDecl *rd = ty->getAsRecordDecl()) {
+        if (const auto *cxxrd = dyn_cast<CXXRecordDecl>(rd);
+            (cxxrd && !cxxrd->hasTrivialDestructor()) ||
+            rd->isNonTrivialToPrimitiveDestroy())
+          cgm.errorNYI(d.getSourceRange(), "emitAutoVarAlloca: set NRVO flag");
+      }
+    } else {
+      // A normal fixed sized variable becomes an alloca in the entry block,
+      mlir::Type allocaTy = convertTypeForMem(ty);
+      // Create the temp alloca and declare variable using it.
+      address = createTempAlloca(allocaTy, alignment, loc, d.getName(),
+                                 /*arraySize=*/nullptr, /*alloca=*/nullptr, ip);
+      declare(address.getPointer(), &d, ty, getLoc(d.getSourceRange()),
+              alignment);
     }
   } else {
-    // A normal fixed sized variable becomes an alloca in the entry block,
-    mlir::Type allocaTy = convertTypeForMem(ty);
-    // Create the temp alloca and declare variable using it.
-    address = createTempAlloca(allocaTy, alignment, loc, d.getName(),
-                               /*arraySize=*/nullptr, /*alloca=*/nullptr, ip);
-    declare(address.getPointer(), &d, ty, getLoc(d.getSourceRange()),
-            alignment);
+    // Non-constant size type
+    assert(!cir::MissingFeatures::openMP());
+    if (!didCallStackSave) {
+      // Save the stack.
+      auto defaultTy = AllocaInt8PtrTy;
+      CharUnits align = CharUnits::fromQuantity(
+          cgm.getDataLayout().getAlignment(defaultTy, false));
+      Address stack = createTempAlloca(defaultTy, align, loc, "saved_stack");
+
+      mlir::Value v = builder.createStackSave(loc, defaultTy);
+      assert(v.getType() == AllocaInt8PtrTy);
+      builder.createStore(loc, v, stack);
+
+      didCallStackSave = true;
+
+      // Push a cleanup block and restore the stack there.
+      // FIXME: in general circumstances, this should be an EH cleanup.
+      pushStackRestore(NormalCleanup, stack);
+    }
+
+    auto vlaSize = getVLASize(ty);
----------------
AmrDeveloper wrote:

```suggestion
    VlaSizePair vlaSize = getVLASize(ty);
```

https://github.com/llvm/llvm-project/pull/163297