r371605 - [Diagnostics] Add -Wsizeof-array-div

[Nico Weber via cfe-commits]

We're looking at turning this one.

One thing that this warns about that's a false positive where we've seen it
is this code for nested arrays:

  float m[4][4];
  for (int i = 0; i < sizeof(m) / sizeof(**m); ++i) (&**m)[i] = 0;

(Why would anyone write code like this? It's a reduced example; consider
e.g. wanting to call std::generate_n() on all elements of a nested array.)

Can we make the warning not fire when dividing the size of a nested array
by the size of the deepest base type?

On Wed, Sep 11, 2019 at 6:58 AM David Bolvansky via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Author: xbolva00
> Date: Wed Sep 11 03:59:47 2019
> New Revision: 371605
>
> URL: http://llvm.org/viewvc/llvm-project?rev=371605&view=rev
> Log:
> [Diagnostics] Add -Wsizeof-array-div
>
> Summary: Clang version of https://www.viva64.com/en/examples/v706/
>
> Reviewers: rsmith
>
> Differential Revision: https://reviews.llvm.org/D67287
>
> Added:
>     cfe/trunk/test/Sema/div-sizeof-array.cpp
> Modified:
>     cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>     cfe/trunk/lib/Sema/SemaExpr.cpp
>
> Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=371605&r1=371604&r2=371605&view=diff
>
> ==============================================================================
> --- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
> +++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Wed Sep 11
> 03:59:47 2019
> @@ -3406,6 +3406,10 @@ def note_pointer_declared_here : Note<
>  def warn_division_sizeof_ptr : Warning<
>    "'%0' will return the size of the pointer, not the array itself">,
>    InGroup<DiagGroup<"sizeof-pointer-div">>;
> +def warn_division_sizeof_array : Warning<
> +  "expression does not compute the number of elements in this array;
> element "
> +  "type is %0, not %1">,
> +  InGroup<DiagGroup<"sizeof-array-div">>;
>
>  def note_function_warning_silence : Note<
>      "prefix with the address-of operator to silence this warning">;
>
> Modified: cfe/trunk/lib/Sema/SemaExpr.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaExpr.cpp?rev=371605&r1=371604&r2=371605&view=diff
>
> ==============================================================================
> --- cfe/trunk/lib/Sema/SemaExpr.cpp (original)
> +++ cfe/trunk/lib/Sema/SemaExpr.cpp Wed Sep 11 03:59:47 2019
> @@ -9158,17 +9158,28 @@ static void DiagnoseDivisionSizeofPointe
>    else
>      RHSTy = RUE->getArgumentExpr()->IgnoreParens()->getType();
>
> -  if (!LHSTy->isPointerType() || RHSTy->isPointerType())
> -    return;
> -  if (LHSTy->getPointeeType().getCanonicalType().getUnqualifiedType() !=
> -      RHSTy.getCanonicalType().getUnqualifiedType())
> -    return;
> +  if (LHSTy->isPointerType() && !RHSTy->isPointerType()) {
> +    if (!S.Context.hasSameUnqualifiedType(LHSTy->getPointeeType(), RHSTy))
> +      return;
>
> -  S.Diag(Loc, diag::warn_division_sizeof_ptr) << LHS <<
> LHS->getSourceRange();
> -  if (const auto *DRE = dyn_cast<DeclRefExpr>(LHSArg)) {
> -    if (const ValueDecl *LHSArgDecl = DRE->getDecl())
> -      S.Diag(LHSArgDecl->getLocation(), diag::note_pointer_declared_here)
> -          << LHSArgDecl;
> +    S.Diag(Loc, diag::warn_division_sizeof_ptr) << LHS <<
> LHS->getSourceRange();
> +    if (const auto *DRE = dyn_cast<DeclRefExpr>(LHSArg)) {
> +      if (const ValueDecl *LHSArgDecl = DRE->getDecl())
> +        S.Diag(LHSArgDecl->getLocation(),
> diag::note_pointer_declared_here)
> +            << LHSArgDecl;
> +    }
> +  } else if (const auto *ArrayTy = S.Context.getAsArrayType(LHSTy)) {
> +    QualType ArrayElemTy = ArrayTy->getElementType();
> +    if (ArrayElemTy->isDependentType() || RHSTy->isDependentType() ||
> +        S.Context.getTypeSize(ArrayElemTy) ==
> S.Context.getTypeSize(RHSTy))
> +      return;
> +    S.Diag(Loc, diag::warn_division_sizeof_array)
> +        << LHSArg->getSourceRange() << ArrayElemTy << RHSTy;
> +    if (const auto *DRE = dyn_cast<DeclRefExpr>(LHSArg)) {
> +      if (const ValueDecl *LHSArgDecl = DRE->getDecl())
> +        S.Diag(LHSArgDecl->getLocation(), diag::note_array_declared_here)
> +            << LHSArgDecl;
> +    }
>    }
>  }
>
>
> Added: cfe/trunk/test/Sema/div-sizeof-array.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/div-sizeof-array.cpp?rev=371605&view=auto
>
> ==============================================================================
> --- cfe/trunk/test/Sema/div-sizeof-array.cpp (added)
> +++ cfe/trunk/test/Sema/div-sizeof-array.cpp Wed Sep 11 03:59:47 2019
> @@ -0,0 +1,28 @@
> +// RUN: %clang_cc1 %s -verify -Wsizeof-array-div -fsyntax-only
> +
> +template <typename Ty, int N>
> +int f(Ty (&Array)[N]) {
> +  return sizeof(Array) / sizeof(Ty); // Should not warn
> +}
> +
> +typedef int int32;
> +
> +void test(void) {
> +  int arr[12];                // expected-note 2 {{array 'arr' declared
> here}}
> +  unsigned long long arr2[4];
> +  int *p = &arr[0];
> +  int a1 = sizeof(arr) / sizeof(*arr);
> +  int a2 = sizeof arr / sizeof p; // expected-warning {{expression does
> not compute the number of elements in this array; element type is 'int',
> not 'int *'}}
> +  int a4 = sizeof arr2 / sizeof p;
> +  int a5 = sizeof(arr) / sizeof(short); // expected-warning {{expression
> does not compute the number of elements in this array; element type is
> 'int', not 'short'}}
> +  int a6 = sizeof(arr) / sizeof(int32);
> +  int a7 = sizeof(arr) / sizeof(int);
> +  int a9 = sizeof(arr) / sizeof(unsigned int);
> +  const char arr3[2] = "A";
> +  int a10 = sizeof(arr3) / sizeof(char);
> +
> +  int arr4[10][12];                         // expected-note 3 {{array
> 'arr4' declared here}}
> +  int b1 = sizeof(arr4) / sizeof(arr2[12]); // expected-warning
> {{expression does not compute the number of elements in this array; element
> type is 'int [12]', not 'unsigned long long'}}
> +  int b2 = sizeof(arr4) / sizeof(int *);    // expected-warning
> {{expression does not compute the number of elements in this array; element
> type is 'int [12]', not 'int *'}}
> +  int b3 = sizeof(arr4) / sizeof(short *);  // expected-warning
> {{expression does not compute the number of elements in this array; element
> type is 'int [12]', not 'short *'}}
> +}
>
>
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