https://github.com/anutosh491 created
https://github.com/llvm/llvm-project/pull/169989
We can see the following while running clang-repl in C mode
```
anutosh491@vv-nuc:/build/anutosh491/llvm-project/build/bin$ ./clang-repl
--Xcc=-x --Xcc=c --Xcc=-std=c23
clang-repl> printf("hi\n");
In file included from <<< inputs >>>:1:
input_line_1:1:1: error: call to undeclared library function 'printf' with type
'int (const char *, ...)'; ISO C99 and
later do not support implicit function declarations
[-Wimplicit-function-declaration]
1 | printf("hi\n");
| ^
input_line_1:1:1: note: include the header <stdio.h> or explicitly provide a
declaration for 'printf'
error: Parsing failed.
clang-repl> #include <stdio.h>
hi
```
In debug mode while dumping the generated Module, i see this
```
clang-repl> printf("hi\n");
In file included from <<< inputs >>>:1:
input_line_1:1:1: error: call to undeclared library function 'printf' with type
'int (const char *, ...)'; ISO C99 and
later do not support implicit function declarations
[-Wimplicit-function-declaration]
1 | printf("hi\n");
| ^
input_line_1:1:1: note: include the header <stdio.h> or explicitly provide a
declaration for 'printf'
error: Parsing failed.
clang-repl> #include <stdio.h>
=== compile-ptu 1 ===
[TU=0x55556cfbf830, M=0x55556cfc13a0 (incr_module_1)]
[LLVM IR]
; ModuleID = 'incr_module_1'
source_filename = "incr_module_1"
target datalayout =
"e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@.str = private unnamed_addr constant [4 x i8] c"hi\0A\00", align 1
@llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr
} { i32 65535, ptr @_GLOBAL__sub_I_incr_module_1, ptr null }]
define internal void @__stmts__0() #0 {
entry:
%call = call i32 (ptr, ...) @printf(ptr noundef @.str)
ret void
}
declare i32 @printf(ptr noundef, ...) #1
; Function Attrs: noinline nounwind uwtable
define internal void @_GLOBAL__sub_I_incr_module_1() #2 section ".text.startup"
{
entry:
call void @__stmts__0()
ret void
}
attributes #0 = { "min-legal-vector-width"="0" }
attributes #1 = { "frame-pointer"="all" "no-trapping-math"="true"
"stack-protector-buffer-size"="8" "target-cpu"="x86-64"
"target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
attributes #2 = { noinline nounwind uwtable "frame-pointer"="all"
"min-legal-vector-width"="0" "no-trapping-math"="true"
"stack-protector-buffer-size"="8" "target-cpu"="x86-64"
"target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
!llvm.module.flags = !{!0, !1, !2, !3, !4}
!llvm.ident = !{!5}
!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{i32 8, !"PIC Level", i32 2}
!2 = !{i32 7, !"PIE Level", i32 2}
!3 = !{i32 7, !"uwtable", i32 2}
!4 = !{i32 7, !"frame-pointer", i32 2}
!5 = !{!"clang version 22.0.0git
(https://github.com/anutosh491/llvm-project.git
81ad8fbc2bb09bae61ed59316468011e4a42cf47)"}
=== end compile-ptu ===
execute-ptu 1: [TU=0x55556cfbf830, M=0x55556cfc13a0 (incr_module_1)]
hi
```
Basically I see that CodeGen emits IR for a cell before we know whether
DiagnosticsEngine has an error. For C code like `printf("hi\n");` without
<stdio.h>, Sema emits a diagnostic but still produces a "codegen-able"
`TopLevelStmt`, so the `printf` call is IR-generated into the current module.
Previously, when `Diags.hasErrorOccurred()` was true, we only cleaned up the
PTU AST and left the CodeGen module untouched. The next successful cell then
called `GenModule()`, which returned that same module (now also containing the
next cell’s IR), causing side effects from the failed cell (e.g. printf)
>From a6c9ac10aca449bee2fdebd8e0ec9fe7d363d0ad Mon Sep 17 00:00:00 2001
From: anutosh491 <[email protected]>
Date: Sat, 29 Nov 2025 16:41:56 +0530
Subject: [PATCH] Drop CodeGen module when an input has parse errors
---
clang/lib/Interpreter/IncrementalAction.cpp | 11 +++++++++++
clang/lib/Interpreter/IncrementalAction.h | 2 ++
clang/lib/Interpreter/IncrementalParser.cpp | 1 +
3 files changed, 14 insertions(+)
diff --git a/clang/lib/Interpreter/IncrementalAction.cpp
b/clang/lib/Interpreter/IncrementalAction.cpp
index 3d489fce54bc6..e2b9d13017ada 100644
--- a/clang/lib/Interpreter/IncrementalAction.cpp
+++ b/clang/lib/Interpreter/IncrementalAction.cpp
@@ -120,6 +120,17 @@ std::unique_ptr<llvm::Module>
IncrementalAction::GenModule() {
return nullptr;
}
+void IncrementalAction::discardCurrentCodeGenModule() {
+ if (CodeGenerator *CG = getCodeGen()) {
+ if (auto *CurM = CG->GetModule()) {
+ llvm::LLVMContext &Ctx = CurM->getContext();
+ std::string Name = CurM->getName().str();
+ std::unique_ptr<llvm::Module> Dead(CG->ReleaseModule());
+ CG->StartModule(Name, Ctx);
+ }
+ }
+}
+
CodeGenerator *IncrementalAction::getCodeGen() const {
FrontendAction *WrappedAct = getWrapped();
if (!WrappedAct || !WrappedAct->hasIRSupport())
diff --git a/clang/lib/Interpreter/IncrementalAction.h
b/clang/lib/Interpreter/IncrementalAction.h
index 725cdd0c27cf4..485cfaa45f793 100644
--- a/clang/lib/Interpreter/IncrementalAction.h
+++ b/clang/lib/Interpreter/IncrementalAction.h
@@ -74,6 +74,8 @@ class IncrementalAction : public WrapperFrontendAction {
/// Generate an LLVM module for the most recent parsed input.
std::unique_ptr<llvm::Module> GenModule();
+
+ void discardCurrentCodeGenModule();
};
class InProcessPrintingASTConsumer final : public MultiplexConsumer {
diff --git a/clang/lib/Interpreter/IncrementalParser.cpp
b/clang/lib/Interpreter/IncrementalParser.cpp
index bf08911e23533..53379603c26da 100644
--- a/clang/lib/Interpreter/IncrementalParser.cpp
+++ b/clang/lib/Interpreter/IncrementalParser.cpp
@@ -82,6 +82,7 @@ IncrementalParser::ParseOrWrapTopLevelDecl() {
DiagnosticsEngine &Diags = S.getDiagnostics();
if (Diags.hasErrorOccurred()) {
+ Act->discardCurrentCodeGenModule();
CleanUpPTU(C.getTranslationUnitDecl());
Diags.Reset(/*soft=*/true);
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