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

[Timm Baeder via cfe-commits]

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

The previous code made this a compile-time decision but it's not.

>From ba9edf8e883d9ac976a79c4f8883d71625b6cbaa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Sun, 18 Aug 2024 15:40:05 +0200
Subject: [PATCH] [clang][bytecode] Fix 'if consteval' in non-constant contexts

The previous code made this a compile-time decision but it's not.
---
 clang/lib/AST/ByteCode/Compiler.cpp          | 20 +++++++++++++-------
 clang/lib/AST/ByteCode/Interp.h              |  5 +++++
 clang/lib/AST/ByteCode/Opcodes.td            |  2 ++
 clang/test/CodeGenCXX/cxx2b-consteval-if.cpp |  1 +
 4 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index c3ecaa40b86f2a..06e66f8d9ef2fa 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -4355,11 +4355,6 @@ bool Compiler<Emitter>::visitReturnStmt(const ReturnStmt *RS) {
 }
 
 template <class Emitter> bool Compiler<Emitter>::visitIfStmt(const IfStmt *IS) {
-  if (IS->isNonNegatedConsteval())
-    return visitStmt(IS->getThen());
-  if (IS->isNegatedConsteval())
-    return IS->getElse() ? visitStmt(IS->getElse()) : true;
-
   if (auto *CondInit = IS->getInit())
     if (!visitStmt(CondInit))
       return false;
@@ -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->emitInvBool(IS))
+      return false;
+  } else {
+    if (!this->visitBool(IS->getCond()))
+      return false;
+  }
 
   if (const Stmt *Else = IS->getElse()) {
     LabelTy LabelElse = this->getLabel();
diff --git a/clang/lib/AST/ByteCode/Interp.h b/clang/lib/AST/ByteCode/Interp.h
index 6cb7a42482ab25..02dff753062dc8 100644
--- a/clang/lib/AST/ByteCode/Interp.h
+++ b/clang/lib/AST/ByteCode/Interp.h
@@ -3054,6 +3054,11 @@ static inline bool Free(InterpState &S, CodePtr OpPC, bool DeleteIsArrayForm) {
                              BlockDesc, Source);
 }
 
+static inline bool IsConstantContext(InterpState &S, CodePtr OpPC) {
+  S.Stk.push<Boolean>(Boolean::from(S.inConstantContext()));
+  return true;
+}
+
 inline bool CheckLiteralType(InterpState &S, CodePtr OpPC, const Type *T) {
   assert(T);
   assert(!S.getLangOpts().CPlusPlus23);
diff --git a/clang/lib/AST/ByteCode/Opcodes.td b/clang/lib/AST/ByteCode/Opcodes.td
index 3478eb174e518e..21bc31bfc5706e 100644
--- a/clang/lib/AST/ByteCode/Opcodes.td
+++ b/clang/lib/AST/ByteCode/Opcodes.td
@@ -787,3 +787,5 @@ def AllocCN : Opcode {
 def Free : Opcode {
   let Args = [ArgBool];
 }
+
+def IsConstantContext: Opcode;
diff --git a/clang/test/CodeGenCXX/cxx2b-consteval-if.cpp b/clang/test/CodeGenCXX/cxx2b-consteval-if.cpp
index 343b6a0bbd8a6b..a6aa862b975ebe 100644
--- a/clang/test/CodeGenCXX/cxx2b-consteval-if.cpp
+++ b/clang/test/CodeGenCXX/cxx2b-consteval-if.cpp
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -std=c++23 %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -std=c++23 %s -emit-llvm -o - -fexperimental-new-constant-interpreter | FileCheck %s
 
 void should_be_used_1();
 void should_be_used_2();