r374035 - [Diagnostics] Silence -Wsizeof-array-div for character buffers

[James Clarke via cfe-commits]

Author: jrtc27
Date: Tue Oct  8 04:34:02 2019
New Revision: 374035

URL: http://llvm.org/viewvc/llvm-project?rev=374035&view=rev
Log:
[Diagnostics] Silence -Wsizeof-array-div for character buffers

Summary:
Character buffers are sometimes used to represent a pool of memory that
contains non-character objects, due to them being synonymous with a stream of
bytes on almost all modern architectures. Often, when interacting with hardware
devices, byte buffers are therefore used as an intermediary and so we can end
Character buffers are sometimes used to represent a pool of memory that
contains non-character objects, due to them being synonymous with a stream of
bytes on almost all modern architectures. Often, when interacting with hardware
devices, byte buffers are therefore used as an intermediary and so we can end
up generating lots of false-positives.

Moreover, due to the ability of character pointers to alias non-character
pointers, the strict aliasing violations that would generally be implied by the
calculations caught by the warning (if the calculation itself is in fact
correct) do not apply here, and so although the length calculation may be
wrong, that is the only possible issue.

Reviewers: rsmith, xbolva00, thakis

Reviewed By: xbolva00, thakis

Subscribers: thakis, lebedev.ri, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D68526

Modified:
    cfe/trunk/lib/Sema/SemaExpr.cpp
    cfe/trunk/test/Sema/div-sizeof-array.cpp

Modified: cfe/trunk/lib/Sema/SemaExpr.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaExpr.cpp?rev=374035&r1=374034&r2=374035&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaExpr.cpp (original)
+++ cfe/trunk/lib/Sema/SemaExpr.cpp Tue Oct  8 04:34:02 2019
@@ -9197,6 +9197,7 @@ static void DiagnoseDivisionSizeofPointe
     QualType ArrayElemTy = ArrayTy->getElementType();
     if (ArrayElemTy != S.Context.getBaseElementType(ArrayTy) ||
         ArrayElemTy->isDependentType() || RHSTy->isDependentType() ||
+        ArrayElemTy->isCharType() ||
         S.Context.getTypeSize(ArrayElemTy) == S.Context.getTypeSize(RHSTy))
       return;
     S.Diag(Loc, diag::warn_division_sizeof_array)

Modified: cfe/trunk/test/Sema/div-sizeof-array.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/div-sizeof-array.cpp?rev=374035&r1=374034&r2=374035&view=diff
==============================================================================
--- cfe/trunk/test/Sema/div-sizeof-array.cpp (original)
+++ cfe/trunk/test/Sema/div-sizeof-array.cpp Tue Oct  8 04:34:02 2019
@@ -25,6 +25,8 @@ void test(void) {
   int a10 = sizeof(arr3) / sizeof(char);
   int a11 = sizeof(arr2) / (sizeof(unsigned));
   int a12 = sizeof(arr) / (sizeof(short));
+  int a13 = sizeof(arr3) / sizeof(p);
+  int a14 = sizeof(arr3) / sizeof(int);
 
   int arr4[10][12];
   int b1 = sizeof(arr4) / sizeof(arr2[12]);