[clang] 006c49d - Change behavior with zero-sized static array extents

[Aaron Ballman via cfe-commits]

Author: Aaron Ballman
Date: 2020-07-10T15:58:11-04:00
New Revision: 006c49d890da633d1ce502117fc2a49863cd65b7

URL: https://github.com/llvm/llvm-project/commit/006c49d890da633d1ce502117fc2a49863cd65b7
DIFF: https://github.com/llvm/llvm-project/commit/006c49d890da633d1ce502117fc2a49863cd65b7.diff

LOG: Change behavior with zero-sized static array extents

Currently, Clang previously diagnosed this code by default:
  void f(int a[static 0]);
saying that "static has no effect on zero-length arrays", which was
accurate.

However, static array extents require that the caller of the function
pass a nonnull pointer to an array of *at least* that number of
elements, but it can pass more (see C17 6.7.6.3p6). Given that we allow
zero-sized arrays as a GNU extension and that it's valid to pass more
elements than specified by the static array extent, we now support
zero-sized static array extents with the usual semantics because it can
be useful in cases like:

  void my_bzero(char p[static 0], int n);
  my_bzero(&c+1, 0); //ok
  my_bzero(t+k,n-k); //ok, pattern from actual code

Added: 
    

Modified: 
    clang/include/clang/Basic/DiagnosticSemaKinds.td
    clang/lib/CodeGen/CGCall.cpp
    clang/lib/Sema/SemaType.cpp
    clang/test/CodeGen/vla.c
    clang/test/Sema/static-array.c

Removed: 
    


################################################################################
diff  --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 29408be6881f..24e942037ecf 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -5395,9 +5395,6 @@ def ext_typecheck_zero_array_size : Extension<
   "zero size arrays are an extension">, InGroup<ZeroLengthArray>;
 def err_typecheck_zero_array_size : Error<
   "zero-length arrays are not permitted in C++">;
-def warn_typecheck_zero_static_array_size : Warning<
-  "'static' has no effect on zero-length arrays">,
-  InGroup<ArrayBounds>;
 def err_array_size_non_int : Error<"size of array has non-integer type %0">;
 def err_init_element_not_constant : Error<
   "initializer element is not a compile-time constant">;

diff  --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 7af986981e5b..e8235c775d8f 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -2504,9 +2504,11 @@ void CodeGenFunction::EmitFunctionProlog(const CGFunctionInfo &FI,
                   ArrSize) {
                 llvm::AttrBuilder Attrs;
                 Attrs.addDereferenceableAttr(
-                  getContext().getTypeSizeInChars(ETy).getQuantity()*ArrSize);
+                    getContext().getTypeSizeInChars(ETy).getQuantity() *
+                    ArrSize);
                 AI->addAttrs(Attrs);
-              } else if (getContext().getTargetAddressSpace(ETy) == 0 &&
+              } else if (getContext().getTargetInfo().getNullPointerValue(
+                             ETy.getAddressSpace()) == 0 &&
                          !CGM.getCodeGenOpts().NullPointerIsValid) {
                 AI->addAttr(llvm::Attribute::NonNull);
               }

diff  --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index b8a787f010d6..b8f7f1a58159 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -2393,13 +2393,6 @@ QualType Sema::BuildArrayType(QualType T, ArrayType::ArraySizeModifier ASM,
                                          ? diag::err_typecheck_zero_array_size
                                          : diag::ext_typecheck_zero_array_size)
           << ArraySize->getSourceRange();
-
-      if (ASM == ArrayType::Static) {
-        Diag(ArraySize->getBeginLoc(),
-             diag::warn_typecheck_zero_static_array_size)
-            << ArraySize->getSourceRange();
-        ASM = ArrayType::Normal;
-      }
     } else if (!T->isDependentType() && !T->isVariablyModifiedType() &&
                !T->isIncompleteType() && !T->isUndeducedType()) {
       // Is the array too large?

diff  --git a/clang/test/CodeGen/vla.c b/clang/test/CodeGen/vla.c
index 37243cd17290..16b82f4acc7d 100644
--- a/clang/test/CodeGen/vla.c
+++ b/clang/test/CodeGen/vla.c
@@ -206,3 +206,7 @@ void test9(int n, int a[static n]) { }
 // NULL-INVALID: define void @test9(i32 %n, i32* nonnull %a)
 // NULL-VALID: define void @test9(i32 %n, i32* %a)
 
+// Make sure a zero-sized static array extent is still required to be nonnull.
+void test10(int a[static 0]) {}
+// NULL-INVALID: define void @test10(i32* nonnull %a)
+// NULL-VALID: define void @test10(i32* %a)

diff  --git a/clang/test/Sema/static-array.c b/clang/test/Sema/static-array.c
index cc1043fe9c47..ef070718dc63 100644
--- a/clang/test/Sema/static-array.c
+++ b/clang/test/Sema/static-array.c
@@ -1,6 +1,7 @@
-// RUN: %clang_cc1 -triple x86_64-apple-macosx10.14.0 -fsyntax-only -fblocks -verify %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.14.0 -fsyntax-only -fblocks -pedantic -verify %s
 
-void cat0(int a[static 0]) {} // expected-warning {{'static' has no effect on zero-length arrays}}
+void cat0(int a[static 0]) {} // expected-warning {{zero size arrays are an extension}} \
+                              // expected-note {{callee declares array parameter as static here}}
 
 void cat(int a[static 3]) {} // expected-note 4 {{callee declares array parameter as static here}} expected-note 2 {{passing argument to parameter 'a' here}}
 
@@ -9,7 +10,7 @@ void vat(int i, int a[static i]) {} // expected-note {{callee declares array par
 void f(int *p) {
   int a[2], b[3], c[4];
 
-  cat0(0);
+  cat0(0); // expected-warning {{null passed to a callee that requires a non-null argument}}
 
   cat(0); // expected-warning {{null passed to a callee that requires a non-null argument}}
   cat(a); // expected-warning {{array argument is too small; contains 2 elements, callee requires at least 3}}