[clang] [C23] Implement N3018: The constexpr specifier for object definitions (PR #73099)

[Aaron Ballman via cfe-commits]

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@@ -14240,6 +14294,114 @@ StmtResult Sema::ActOnCXXForRangeIdentifier(Scope *S, SourceLocation IdentLoc,
                                                       : IdentLoc);
 }
 
+static ImplicitConversionKind getConversionKind(QualType FromType,
+                                                QualType ToType) {
+  if (ToType->isIntegerType()) {
+    if (FromType->isComplexType())
+      return ICK_Complex_Real;
+    if (FromType->isFloatingType())
+      return ICK_Floating_Integral;
+    if (FromType->isIntegerType())
+      return ICK_Integral_Conversion;
+  }
+
+  if (ToType->isFloatingType()) {
+    if (FromType->isComplexType())
+      return ICK_Complex_Real;
+    if (FromType->isFloatingType())
+      return ICK_Floating_Conversion;
+    if (FromType->isIntegerType())
+      return ICK_Floating_Integral;
+  }
+
+  return ICK_Identity;
+}
+
+static bool checkC23ConstexprInitConversion(Sema &S, const Expr *Init) {
+  assert(S.getLangOpts().C23);
+  const Expr *InitNoCast = Init->IgnoreImpCasts();
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AaronBallman wrote:

We probably want to ignore paren expressions as well.

https://github.com/llvm/llvm-project/pull/73099