[clang] [NFC][Clang] Avoid potential null pointer dereferences in Sema::AddInitializerToDecl(). (PR #106235)

[Tom Honermann via cfe-commits]

https://github.com/tahonermann created https://github.com/llvm/llvm-project/pull/106235

Control flow analysis performed by a static analysis tool revealed the potential for null pointer dereferences to occur in conjunction with the `Init` parameter in `Sema::AddInitializerToDecl()`. On entry to the function, `Init` is required to be non-null as there are multiple potential branches that unconditionally dereference it. However, there were two places where `Init` is compared to null thus implying that `Init` is expected to be null in some cases. These checks appear to be purely defensive checks and thus unnecessary. Further, there were several cases where code checked `Result`, a variable of type `ExprResult`, for an invalid value, but did not check for a valid but null value and then proceeded to unconditionally dereference the potential null result. This change elides the unnecessary defensive checks and changes some checks for an invalid result to instead branch on an unusable result (either an invalid result or a valid but null result).

>From 787efaec5a565d118cacd306c91ed002bea7a992 Mon Sep 17 00:00:00 2001
From: Tom Honermann <tom.honermann at intel.com>
Date: Sun, 25 Aug 2024 11:33:29 -0700
Subject: [PATCH] [NFC][Clang] Avoid potential null pointer dereferences in
 Sema::AddInitializerToDecl().

Control flow analysis performed by a static analysis tool revealed the potential
for null pointer dereferences to occur in conjunction with the `Init` parameter
in Sema::AddInitializerToDecl(). On entry to the function, `Init` is required to
be non-null as there are multiple potential branches that unconditionally
dereference it. However, there were two places where `Init` is compared to null
thus implying that `Init` is expected to be null in some cases. These checks
appear to be purely defensive checks and thus unnecessary. Further, there were
several cases where code checked `Result`, a variable of type `ExprResult`, for
an invalid value, but did not check for a valid but null value and then
proceeded to unconditionally dereference the potential null result. This change
elides the unnecessary defensive checks and changes some checks for an invalid
result to instead branch on an unusable result (either an invalid result or a
valid but null result).
---
 clang/lib/Sema/SemaDecl.cpp | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index b0ccbbe34b70c3..c643d4fbbba0eb 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -13319,7 +13319,7 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
   }
 
   // WebAssembly tables can't be used to initialise a variable.
-  if (Init && !Init->getType().isNull() &&
+  if (!Init->getType().isNull() &&
       Init->getType()->isWebAssemblyTableType()) {
     Diag(Init->getExprLoc(), diag::err_wasm_table_art) << 0;
     VDecl->setInvalidDecl();
@@ -13463,7 +13463,7 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
   if (getLangOpts().DebuggerCastResultToId && DclT->isObjCObjectPointerType() &&
       Init->getType() == Context.UnknownAnyTy) {
     ExprResult Result = forceUnknownAnyToType(Init, Context.getObjCIdType());
-    if (Result.isInvalid()) {
+    if (!Result.isUsable()) {
       VDecl->setInvalidDecl();
       return;
     }
@@ -13491,7 +13491,7 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
             InitializationSequence Init(*this, Entity, Kind, MultiExprArg(E));
             return Init.Failed() ? ExprError() : E;
           });
-      if (Res.isInvalid()) {
+      if (!Res.isUsable()) {
         VDecl->setInvalidDecl();
       } else if (Res.get() != Args[Idx]) {
         Args[Idx] = Res.get();
@@ -13504,7 +13504,7 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
                                    /*TopLevelOfInitList=*/false,
                                    /*TreatUnavailableAsInvalid=*/false);
     ExprResult Result = InitSeq.Perform(*this, Entity, Kind, Args, &DclT);
-    if (Result.isInvalid()) {
+    if (!Result.isUsable()) {
       // If the provided initializer fails to initialize the var decl,
       // we attach a recovery expr for better recovery.
       auto RecoveryExpr =
@@ -13528,7 +13528,7 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
                       InitSeq.step_begin()->Kind ==
                           InitializationSequence::SK_ParenthesizedListInit;
     QualType VDeclType = VDecl->getType();
-    if (Init && !Init->getType().isNull() &&
+    if (!Init->getType().isNull() &&
         !Init->getType()->isDependentType() && !VDeclType->isDependentType() &&
         Context.getAsIncompleteArrayType(VDeclType) &&
         Context.getAsIncompleteArrayType(Init->getType())) {
@@ -13592,7 +13592,7 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
   ExprResult Result =
       ActOnFinishFullExpr(Init, VDecl->getLocation(),
                           /*DiscardedValue*/ false, VDecl->isConstexpr());
-  if (Result.isInvalid()) {
+  if (!Result.isUsable()) {
     VDecl->setInvalidDecl();
     return;
   }