[clang] [clang][bytecode] Fix 'if consteval' in non-constant contexts (PR #104707)

[Timm Baeder via cfe-commits]

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@@ -4368,8 +4363,19 @@ template <class Emitter> bool Compiler<Emitter>::visitIfStmt(const IfStmt *IS) {
     if (!visitDeclStmt(CondDecl))
       return false;
 
-  if (!this->visitBool(IS->getCond()))
-    return false;
+  // Compile condition.
+  if (IS->isNonNegatedConsteval()) {
+    if (!this->emitIsConstantContext(IS))
+      return false;
+  } else if (IS->isNegatedConsteval()) {
+    if (!this->emitIsConstantContext(IS))
+      return false;
+    if (!this->emitInv(IS))
+      return false;
+  } else {
+    if (!this->visitBool(IS->getCond()))
+      return false;
+  }
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tbaederr wrote:

Only if that has truly not been implemented yet. Otherwise, we need to always diagnose it anyway, in the same way we do for regular if statements.

https://github.com/llvm/llvm-project/pull/104707