[Sema] atomic_compare_exchange: check failure memory order (#74959)

For

`__atomic_compare_exchange{,_n}/__c11_atomic_compare_exchange_{strong,weak}`,
GCC checks both the success memory order and the failure memory order
under the default -Winvalid-memory-model ("memory model" is confusing
here and "memory order" is much more common in the atomic context).

* The failure memory order, if a constant, must be one of
  relaxed/consume/acquire/seq_cst.

Clang checks just the success memory order under the default
-Watomic-memory-ordering. This patch checks the failure memory order.

1 files changed, 26 insertions, 8 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 254c272..bcddaa1 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -5030,14 +5030,14 @@ bool Sema::CheckAMDGCNBuiltinFunctionCall(unsigned BuiltinID,
   if (!llvm::isValidAtomicOrderingCABI(Ord))
     return Diag(ArgExpr->getBeginLoc(),
                 diag::warn_atomic_op_has_invalid_memory_order)
-           << ArgExpr->getSourceRange();
+           << 0 << ArgExpr->getSourceRange();
   switch (static_cast<llvm::AtomicOrderingCABI>(Ord)) {
   case llvm::AtomicOrderingCABI::relaxed:
   case llvm::AtomicOrderingCABI::consume:
     if (BuiltinID == AMDGPU::BI__builtin_amdgcn_fence)
       return Diag(ArgExpr->getBeginLoc(),
                   diag::warn_atomic_op_has_invalid_memory_order)
-             << ArgExpr->getSourceRange();
+             << 0 << ArgExpr->getSourceRange();
     break;
   case llvm::AtomicOrderingCABI::acquire:
   case llvm::AtomicOrderingCABI::release:
@@ -8177,13 +8177,31 @@ ExprResult Sema::BuildAtomicExpr(SourceRange CallRange, SourceRange ExprRange,
     break;
   }
 
+  // If the memory orders are constants, check they are valid.
   if (SubExprs.size() >= 2 && Form != Init) {
-    if (std::optional<llvm::APSInt> Result =
-            SubExprs[1]->getIntegerConstantExpr(Context))
-      if (!isValidOrderingForOp(Result->getSExtValue(), Op))
-        Diag(SubExprs[1]->getBeginLoc(),
-             diag::warn_atomic_op_has_invalid_memory_order)
-            << SubExprs[1]->getSourceRange();
+    std::optional<llvm::APSInt> Success =
+        SubExprs[1]->getIntegerConstantExpr(Context);
+    if (Success && !isValidOrderingForOp(Success->getSExtValue(), Op)) {
+      Diag(SubExprs[1]->getBeginLoc(),
+           diag::warn_atomic_op_has_invalid_memory_order)
+          << /*success=*/(Form == C11CmpXchg || Form == GNUCmpXchg)
+          << SubExprs[1]->getSourceRange();
+    }
+    if (SubExprs.size() >= 5) {
+      if (std::optional<llvm::APSInt> Failure =
+              SubExprs[3]->getIntegerConstantExpr(Context)) {
+        if (!llvm::is_contained(
+                {llvm::AtomicOrderingCABI::relaxed,
+                 llvm::AtomicOrderingCABI::consume,
+                 llvm::AtomicOrderingCABI::acquire,
+                 llvm::AtomicOrderingCABI::seq_cst},
+                (llvm::AtomicOrderingCABI)Failure->getSExtValue())) {
+          Diag(SubExprs[3]->getBeginLoc(),
+               diag::warn_atomic_op_has_invalid_memory_order)
+              << /*failure=*/2 << SubExprs[3]->getSourceRange();
+        }
+      }
+    }
   }
 
   if (auto ScopeModel = AtomicExpr::getScopeModel(Op)) {