[clang] efbf013 - Only issue warning for subtraction involving null pointers on live code paths

[Jamie Schmeiser via cfe-commits]

Author: Jamie Schmeiser
Date: 2022-06-03T10:10:37-04:00
New Revision: efbf0136b4108692ddd1a852b3f5b232c10d2097

URL: https://github.com/llvm/llvm-project/commit/efbf0136b4108692ddd1a852b3f5b232c10d2097
DIFF: https://github.com/llvm/llvm-project/commit/efbf0136b4108692ddd1a852b3f5b232c10d2097.diff

LOG: Only issue warning for subtraction involving null pointers on live code paths

Summary:
Change the warning produced for subtraction from (or with) a null pointer
to only be produced when the code path is live.
https://github.com/llvm/llvm-project/issues/54570

Author: Jamie Schmeiser <schmeise at ca.ibm.com>
Reviewed By: anarazel (Andres Freund)
Differential Revision: https://reviews.llvm.org/D126816

Added: 
    

Modified: 
    clang/lib/Sema/SemaExpr.cpp
    clang/test/Sema/pointer-subtraction.c
    clang/test/Sema/pointer-subtraction.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 3e8bd63e89ae9..6627aaf3e6d88 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -10845,8 +10845,10 @@ static void diagnoseSubtractionOnNullPointer(Sema &S, SourceLocation Loc,
   if (S.Diags.getSuppressSystemWarnings() && S.SourceMgr.isInSystemMacro(Loc))
     return;
 
-  S.Diag(Loc, diag::warn_pointer_sub_null_ptr)
-      << S.getLangOpts().CPlusPlus << Pointer->getSourceRange();
+  S.DiagRuntimeBehavior(Loc, Pointer,
+                        S.PDiag(diag::warn_pointer_sub_null_ptr)
+                            << S.getLangOpts().CPlusPlus
+                            << Pointer->getSourceRange());
 }
 
 /// Diagnose invalid arithmetic on two function pointers.

diff  --git a/clang/test/Sema/pointer-subtraction.c b/clang/test/Sema/pointer-subtraction.c
index c3dbbd47459fa..79d18a0f0a306 100644
--- a/clang/test/Sema/pointer-subtraction.c
+++ b/clang/test/Sema/pointer-subtraction.c
@@ -11,6 +11,16 @@ void a(void) {
   f = (char *)(f - (char *)0);         // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
   f = (char *)((char *)0 - (char *)0); // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}} expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
 
+  if (1)
+    f = (char *)((char *)0 - f);         // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
+  else
+    f = (char *)((char *)0 - f);
+
+  if (0)
+    f = (char *)((char *)0 - f);
+  else
+    f = (char *)((char *)0 - f);         // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
+
 #ifndef SYSTEM_WARNINGS
   SYSTEM_MACRO(f);
 #else

diff  --git a/clang/test/Sema/pointer-subtraction.cpp b/clang/test/Sema/pointer-subtraction.cpp
index efbb3255e5d31..28063a1fea6ef 100644
--- a/clang/test/Sema/pointer-subtraction.cpp
+++ b/clang/test/Sema/pointer-subtraction.cpp
@@ -11,6 +11,16 @@ void a() {
   f = (char *)(f - (char *)0);         // expected-warning {{performing pointer subtraction with a null pointer may have undefined behavior}}
   f = (char *)((char *)0 - (char *)0); // valid in C++
 
+  if (1)
+    f = (char *)((char *)0 - f);         // expected-warning {{performing pointer subtraction with a null pointer may have undefined behavior}}
+  else
+    f = (char *)((char *)0 - f);
+
+  if (0)
+    f = (char *)((char *)0 - f);
+  else
+    f = (char *)((char *)0 - f);         // expected-warning {{performing pointer subtraction with a null pointer may have undefined behavior}}
+
 #ifndef SYSTEM_WARNINGS
   SYSTEM_MACRO(f);
 #else