[clang] [Clang] Implement P2809: Trivial infinite loops are not Undefined Behavior (PR #90066)

[Eli Friedman via cfe-commits]

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@@ -908,6 +908,69 @@ void CodeGenFunction::EmitIfStmt(const IfStmt &S) {
     incrementProfileCounter(&S);
 }
 
+bool CodeGenFunction::checkIfLoopMustProgress(const Expr *ControllingExpression,
+                                              bool HasEmptyBody) {
+  if (CGM.getCodeGenOpts().getFiniteLoops() ==
+      CodeGenOptions::FiniteLoopsKind::Never)
+    return false;
+
+  // Now apply rules for plain C (see  6.8.5.6 in C11).
+  // Loops with constant conditions do not have to make progress in any C
+  // version.
+  // As an extension, we consisider loops whose constant expression
+  // can be constant-folded.
+  Expr::EvalResult Result;
+  bool CondIsConstInt =
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efriedma-quic wrote:

is_constant_evaluated is equivalent to if consteval, i.e. it's true in a context which is manifestly constant-evaluated.  So... is the condition manifestly constant-evaluated in this case?  If it is, that's fine, I guess, but the standard definition of "manifestly constant-evaluated" should probably be amended to reflect that.  Otherwise, I'm not sure how to interpret the standard here; whether an expression is manifestly constant-evaluated changes the way it's represented in the AST.

See also #89565.

https://github.com/llvm/llvm-project/pull/90066