[clang] Remove warnings from -Wchar-subscripts for known positive constants (PR #69061)
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Thu Nov 2 12:46:00 PDT 2023
https://github.com/wheatman updated https://github.com/llvm/llvm-project/pull/69061
>From b46d376e803bae29231e313a623f508e22e6c9d6 Mon Sep 17 00:00:00 2001
From: Brian Wheatman <bwheatman at gmail.com>
Date: Sat, 14 Oct 2023 12:02:19 -0400
Subject: [PATCH] Remove warnings from -Wchar-subscripts for known positive
constants
---
clang/docs/ReleaseNotes.rst | 2 +
clang/lib/Sema/SemaExpr.cpp | 11 ++-
clang/test/Sema/warn-char-subscripts.c | 25 ++++++
clang/test/Sema/warn-char-subscripts.cpp | 103 +++++++++++++++++++++++
4 files changed, 138 insertions(+), 3 deletions(-)
create mode 100644 clang/test/Sema/warn-char-subscripts.cpp
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index be7c8bf247f7af5..4e3d7108f0408cc 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -393,6 +393,8 @@ Bug Fixes in This Version
operator in C. No longer issuing a confusing diagnostic along the lines of
"incompatible operand types ('foo' and 'foo')" with extensions such as matrix
types. Fixes (`#69008 <https://github.com/llvm/llvm-project/issues/69008>`_)
+- Clang's ``-Wchar-subscripts`` no longer warns on chars whose values are known non-negative constants.
+ Fixes (`#18763 <https://github.com/llvm/llvm-project/issues/18763>`_)
Bug Fixes to Compiler Builtins
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index aa30a3a03887558..5c84c8ff146a3f6 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -6018,9 +6018,14 @@ Sema::CreateBuiltinArraySubscriptExpr(Expr *Base, SourceLocation LLoc,
<< IndexExpr->getSourceRange());
if ((IndexExpr->getType()->isSpecificBuiltinType(BuiltinType::Char_S) ||
- IndexExpr->getType()->isSpecificBuiltinType(BuiltinType::Char_U))
- && !IndexExpr->isTypeDependent())
- Diag(LLoc, diag::warn_subscript_is_char) << IndexExpr->getSourceRange();
+ IndexExpr->getType()->isSpecificBuiltinType(BuiltinType::Char_U)) &&
+ !IndexExpr->isTypeDependent()) {
+ std::optional<llvm::APSInt> IntegerContantExpr =
+ IndexExpr->getIntegerConstantExpr(getASTContext());
+ if (!IntegerContantExpr.has_value() ||
+ IntegerContantExpr.value().isNegative())
+ Diag(LLoc, diag::warn_subscript_is_char) << IndexExpr->getSourceRange();
+ }
// C99 6.5.2.1p1: "shall have type "pointer to *object* type". Similarly,
// C++ [expr.sub]p1: The type "T" shall be a completely-defined object
diff --git a/clang/test/Sema/warn-char-subscripts.c b/clang/test/Sema/warn-char-subscripts.c
index 2e72d90fa612aed..0a012f68feae07f 100644
--- a/clang/test/Sema/warn-char-subscripts.c
+++ b/clang/test/Sema/warn-char-subscripts.c
@@ -62,3 +62,28 @@ void t10(void) {
UnsignedCharTy subscript = 0;
int val = array[subscript]; // no warning for unsigned char
}
+
+void t11(void) {
+ int array[256] = { 0 };
+ int val = array['a']; // no warning for char with known positive value
+}
+
+void t12(void) {
+ int array[256] = { 0 };
+ char b = 'a';
+ int val = array[b]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+void t13(void) {
+ int array[256] = { 0 };
+ const char b = 'a';
+ int val = array[b]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+void t14(void) {
+ int array[256] = { 0 }; // expected-note {{array 'array' declared here}}
+ const char b = -1;
+ // expected-warning at +2 {{array subscript is of type 'char'}}
+ // expected-warning at +1 {{array index -1 is before the beginning of the array}}
+ int val = array[b];
+}
diff --git a/clang/test/Sema/warn-char-subscripts.cpp b/clang/test/Sema/warn-char-subscripts.cpp
new file mode 100644
index 000000000000000..929fb372c5173fd
--- /dev/null
+++ b/clang/test/Sema/warn-char-subscripts.cpp
@@ -0,0 +1,103 @@
+// RUN: %clang_cc1 -Wchar-subscripts -fsyntax-only -verify %s
+
+void t1(void) {
+ int array[1] = { 0 };
+ char subscript = 0;
+ int val = array[subscript]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+void t2(void) {
+ int array[1] = { 0 };
+ char subscript = 0;
+ int val = subscript[array]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+void t3(void) {
+ int *array = 0;
+ char subscript = 0;
+ int val = array[subscript]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+void t4(void) {
+ int *array = 0;
+ char subscript = 0;
+ int val = subscript[array]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+char returnsChar(void);
+void t5(void) {
+ int *array = 0;
+ int val = array[returnsChar()]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+void t6(void) {
+ int array[1] = { 0 };
+ signed char subscript = 0;
+ int val = array[subscript]; // no warning for explicit signed char
+}
+
+void t7(void) {
+ int array[1] = { 0 };
+ unsigned char subscript = 0;
+ int val = array[subscript]; // no warning for unsigned char
+}
+
+typedef char CharTy;
+void t8(void) {
+ int array[1] = { 0 };
+ CharTy subscript = 0;
+ int val = array[subscript]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+typedef signed char SignedCharTy;
+void t9(void) {
+ int array[1] = { 0 };
+ SignedCharTy subscript = 0;
+ int val = array[subscript]; // no warning for explicit signed char
+}
+
+typedef unsigned char UnsignedCharTy;
+void t10(void) {
+ int array[1] = { 0 };
+ UnsignedCharTy subscript = 0;
+ int val = array[subscript]; // no warning for unsigned char
+}
+
+void t11(void) {
+ int array[256] = { 0 };
+ int val = array['a']; // no warning for char with known positive value
+}
+
+void t12(void) {
+ int array[256] = { 0 };
+ char b = 'a';
+ int val = array[b]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+void t13(void) {
+ int array[256] = { 0 };
+ const char b = 'a';
+ int val = array[b]; // no warning for char with known positive value
+}
+
+void t14(void) {
+ int array[256] = { 0 };
+ constexpr char b = 'a';
+ int val = array[b]; // no warning for char with known positive value
+}
+
+void t15(void) {
+ int array[256] = { 0 }; // expected-note {{array 'array' declared here}}
+ const char b = -1;
+ // expected-warning at +2 {{array subscript is of type 'char'}}
+ // expected-warning at +1 {{array index -1 is before the beginning of the array}}
+ int val = array[b];
+}
+
+void t16(void) {
+ int array[256] = { 0 }; // expected-note {{array 'array' declared here}}
+ constexpr char b = -1;
+ // expected-warning at +2 {{array subscript is of type 'char'}}
+ // expected-warning at +1 {{array index -1 is before the beginning of the array}}
+ int val = array[b];
+}
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