[clang] f6c54cd - [-Wunsafe-buffer-usage] Ignore array subscript on literal zero

[via cfe-commits]

Author: ziqingluo-90
Date: 2022-12-16T21:04:41-08:00
New Revision: f6c54cdbc4394cd32f0dde990f217ca8f534a136

URL: https://github.com/llvm/llvm-project/commit/f6c54cdbc4394cd32f0dde990f217ca8f534a136
DIFF: https://github.com/llvm/llvm-project/commit/f6c54cdbc4394cd32f0dde990f217ca8f534a136.diff

LOG: [-Wunsafe-buffer-usage] Ignore array subscript on literal zero

Unsafe Buffer Usage analysis only warns unsafe buffer accesses but not
pointer dereferences.  An array subscript on a literal zero is
equivalent to dereference a pointer thus we do not want to warn it.

Reviewed By: NoQ

Differential Revision: https://reviews.llvm.org/D138321

Added: 
    

Modified: 
    clang/lib/Analysis/UnsafeBufferUsage.cpp
    clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Analysis/UnsafeBufferUsage.cpp b/clang/lib/Analysis/UnsafeBufferUsage.cpp
index ba459d2176ad..85449c4c5b1c 100644
--- a/clang/lib/Analysis/UnsafeBufferUsage.cpp
+++ b/clang/lib/Analysis/UnsafeBufferUsage.cpp
@@ -189,9 +189,9 @@ class ArraySubscriptGadget : public UnsafeGadget {
   static Matcher matcher() {
     // FIXME: What if the index is integer literal 0? Should this be
     // a safe gadget in this case?
-    return stmt(
-        arraySubscriptExpr(hasBase(ignoringParenImpCasts(hasPointerType())))
-            .bind(ArraySubscrTag));
+    return stmt(arraySubscriptExpr(hasBase(ignoringParenImpCasts(hasPointerType())),
+                                   unless(hasIndex(integerLiteral(equals(0)))))
+                .bind(ArraySubscrTag));
   }
 
   const ArraySubscriptExpr *getBaseStmt() const override { return ASE; }

diff  --git a/clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp b/clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp
index bff9fd666ac6..9b1481e8a2ed 100644
--- a/clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp
+++ b/clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp
@@ -29,10 +29,10 @@ void * voidPtrCall(void);
 char * charPtrCall(void);
 
 void testArraySubscripts(int *p, int **pp) {
-  foo(p[0],             // expected-warning{{unchecked operation on raw buffer in expression}}
-      pp[0][0],         // expected-warning2{{unchecked operation on raw buffer in expression}}
-      0[0[pp]],         // expected-warning2{{unchecked operation on raw buffer in expression}}
-      0[pp][0]          // expected-warning2{{unchecked operation on raw buffer in expression}}
+  foo(p[1],             // expected-warning{{unchecked operation on raw buffer in expression}}
+      pp[1][1],         // expected-warning2{{unchecked operation on raw buffer in expression}}
+      1[1[pp]],         // expected-warning2{{unchecked operation on raw buffer in expression}}
+      1[pp][1]          // expected-warning2{{unchecked operation on raw buffer in expression}}
       );
 
   if (p[3]) {           // expected-warning{{unchecked operation on raw buffer in expression}}
@@ -50,11 +50,18 @@ void testArraySubscripts(int *p, int **pp) {
   int a[10], b[10][10];
 
   // Not to warn subscripts on arrays
-  foo(a[0], a[1],
-      0[a], 1[a],
+  foo(a[1], 1[a],
       b[3][4],
       4[b][3],
       4[3[b]]);
+
+  // Not to warn when index is zero
+  foo(p[0], pp[0][0], 0[0[pp]], 0[pp][0],
+      ((int*)voidPtrCall())[0],
+      0[(int*)voidPtrCall()],
+      charPtrCall()[0],
+      0[charPtrCall()]
+      );
 }
 
 void testArraySubscriptsWithAuto(int *p, int **pp) {
@@ -62,19 +69,19 @@ void testArraySubscriptsWithAuto(int *p, int **pp) {
 
   auto ap1 = a;
 
-  foo(ap1[0]);  // expected-warning{{unchecked operation on raw buffer in expression}}
+  foo(ap1[1]);  // expected-warning{{unchecked operation on raw buffer in expression}}
 
   auto ap2 = p;
 
-  foo(ap2[0]);  // expected-warning{{unchecked operation on raw buffer in expression}}
+  foo(ap2[1]);  // expected-warning{{unchecked operation on raw buffer in expression}}
 
   auto ap3 = pp;
 
-  foo(ap3[0][0]); // expected-warning2{{unchecked operation on raw buffer in expression}}
+  foo(ap3[1][1]); // expected-warning2{{unchecked operation on raw buffer in expression}}
 
   auto ap4 = *pp;
 
-  foo(ap4[0]);  // expected-warning{{unchecked operation on raw buffer in expression}}
+  foo(ap4[1]);  // expected-warning{{unchecked operation on raw buffer in expression}}
 }
 
 void testUnevaluatedContext(int * p) {