[clang] 94d36fd - Fix a crash on invalid with _Generic expressions

[Aaron Ballman via cfe-commits]

Author: Aaron Ballman
Date: 2022-05-04T12:41:56-04:00
New Revision: 94d36fdbd7d2c6eab250f15f65fd20a6447b92eb

URL: https://github.com/llvm/llvm-project/commit/94d36fdbd7d2c6eab250f15f65fd20a6447b92eb
DIFF: https://github.com/llvm/llvm-project/commit/94d36fdbd7d2c6eab250f15f65fd20a6447b92eb.diff

LOG: Fix a crash on invalid with _Generic expressions

We were failing to check if the controlling expression is dependent or
not when testing whether it has side effects. This would trigger an
assertion. Instead, if the controlling expression is dependent, we
suppress the check and diagnostic.

This fixes Issue 50227.

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/lib/Sema/SemaExpr.cpp
    clang/test/Sema/generic-selection.c

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 74d180053ee81..079523a07361e 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -128,6 +128,10 @@ Bug Fixes
   the functions were 
diff erent. It now diagnoses this case correctly as an
   ambiguous call and an error. Fixes
   `Issue 53640 <https://github.com/llvm/llvm-project/issues/53640>`_.
+- No longer crash when trying to determine whether the controlling expression
+  argument to a generic selection expression has side effects in the case where
+  the expression is result dependent. This fixes
+  `Issue 50227 <https://github.com/llvm/llvm-project/issues/50227>`_.
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

diff  --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 67012527888d3..058967b656bc9 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -1653,18 +1653,18 @@ Sema::CreateGenericSelectionExpr(SourceLocation KeyLoc,
     ControllingExpr = R.get();
   }
 
+  bool TypeErrorFound = false,
+       IsResultDependent = ControllingExpr->isTypeDependent(),
+       ContainsUnexpandedParameterPack
+         = ControllingExpr->containsUnexpandedParameterPack();
+
   // The controlling expression is an unevaluated operand, so side effects are
   // likely unintended.
-  if (!inTemplateInstantiation() &&
+  if (!inTemplateInstantiation() && !IsResultDependent &&
       ControllingExpr->HasSideEffects(Context, false))
     Diag(ControllingExpr->getExprLoc(),
          diag::warn_side_effects_unevaluated_context);
 
-  bool TypeErrorFound = false,
-       IsResultDependent = ControllingExpr->isTypeDependent(),
-       ContainsUnexpandedParameterPack
-         = ControllingExpr->containsUnexpandedParameterPack();
-
   for (unsigned i = 0; i < NumAssocs; ++i) {
     if (Exprs[i]->containsUnexpandedParameterPack())
       ContainsUnexpandedParameterPack = true;

diff  --git a/clang/test/Sema/generic-selection.c b/clang/test/Sema/generic-selection.c
index 82d40afec8a5d..82ba75e1ffc73 100644
--- a/clang/test/Sema/generic-selection.c
+++ b/clang/test/Sema/generic-selection.c
@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -std=c11 -fsyntax-only -Wno-strict-prototypes -verify %s
-// RUN: %clang_cc1 -std=c99 -pedantic -fsyntax-only -Wno-strict-prototypes -verify=expected,ext %s
+// RUN: %clang_cc1 -std=c11 -fsyntax-only -Wno-strict-prototypes -Wno-implicit-function-declaration -verify %s
+// RUN: %clang_cc1 -std=c99 -pedantic -fsyntax-only -Wno-strict-prototypes -Wno-implicit-function-declaration -verify=expected,ext %s
 
 void g(void);
 
@@ -47,3 +47,13 @@ char testc(char);
 void PR30201(void) {
   _Generic(4, char:testc, default:test)(4); // ext-warning {{'_Generic' is a C11 extension}}
 }
+
+void GH50227(void) {
+  // Previously, the controlling expression for the outer _Generic makes it
+  // result dependent, and testing whether that controlling expression has side
+  // effects would cause a crash.
+  _Generic( // ext-warning {{'_Generic' is a C11 extension}}
+    n(
+      _Generic(n++, int : 0) // expected-error {{cannot increment value of type 'int ()'}} ext-warning {{'_Generic' is a C11 extension}}
+    ), int : 0);
+}