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re PR c++/34198 (-Wconversion gives apparent erroneous warning with g++ 4.3-20071109)

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PR c++/34198
	* c-common.c (conversion_warning): For INTEGER_TYPE to
	INTEGER_TYPE conversions call get_narrower on expr to avoid
	spurious warnings from binop shortening or when the implicit
	conversion can't change the value.

	* gcc.dg/Wconversion-5.c: New test.
	* g++.dg/Wconversion3.C: New test.

From-SVN: r130377
This commit is contained in:
Jakub Jelinek 2007-11-23 14:39:44 +01:00 • committed by Jakub Jelinek
parent bb1f5840b5
commit cfdaefecf6
5 changed files with 114 additions and 5 deletions
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8
gcc/ChangeLog
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@ -1,3 +1,11 @@
2007-11-23 Jakub Jelinek <jakub@redhat.com>
PR c++/34198
* c-common.c (conversion_warning): For INTEGER_TYPE to
INTEGER_TYPE conversions call get_narrower on expr to avoid
spurious warnings from binop shortening or when the implicit
conversion can't change the value.
2007-11-22 Joseph Myers <joseph@codesourcery.com>
PR c/14050

35
gcc/c-common.c
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@ -1280,6 +1280,14 @@ conversion_warning (tree type, tree expr)
else if (TREE_CODE (TREE_TYPE (expr)) == INTEGER_TYPE
&& TREE_CODE (type) == INTEGER_TYPE)
{
/* Don't warn about unsigned char y = 0xff, x = (int) y; */
int uns;
tree orig_expr = expr;
expr = get_narrower (expr, &uns);
if (expr == orig_expr)
uns = TYPE_UNSIGNED (TREE_TYPE (expr));
/* Warn for integer types converted to smaller integer types. */
if (formal_prec < TYPE_PRECISION (TREE_TYPE (expr)))
give_warning = true;
@ -1287,14 +1295,31 @@ conversion_warning (tree type, tree expr)
/* When they are the same width but different signedness,
then the value may change. */
else if ((formal_prec == TYPE_PRECISION (TREE_TYPE (expr))
&& TYPE_UNSIGNED (TREE_TYPE (expr)) != TYPE_UNSIGNED (type))
&& uns != TYPE_UNSIGNED (type))
/* Even when converted to a bigger type, if the type is
unsigned but expr is signed, then negative values
will be changed. */
|| (TYPE_UNSIGNED (type) && !TYPE_UNSIGNED (TREE_TYPE (expr))))
warning (OPT_Wsign_conversion,
"conversion to %qT from %qT may change the sign of the result",
type, TREE_TYPE (expr));
|| (TYPE_UNSIGNED (type) && !uns))
{
if (uns != TYPE_UNSIGNED (TREE_TYPE (expr)))
{
/* For signed char s1, s2 = (int) (unsigned char) s1;
get_narrower returns s1, but uns = 1. Find the
narrowest type with uns == TYPE_UNSIGNED (type). */
tree unsexpr = orig_expr;
while (TREE_CODE (unsexpr) == NOP_EXPR
&& unsexpr != expr
&& TYPE_UNSIGNED (TREE_TYPE (TREE_OPERAND (unsexpr,
0)))
== uns)
unsexpr = TREE_OPERAND (unsexpr, 0);
expr = unsexpr;
}
warning (OPT_Wsign_conversion,
"conversion to %qT from %qT may change the sign of the result",
type, TREE_TYPE (expr));
}
}
/* Warn for integer types converted to real types if and only if

6
gcc/testsuite/ChangeLog
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@ -1,3 +1,9 @@
2007-11-23 Jakub Jelinek <jakub@redhat.com>
PR c++/34198
* gcc.dg/Wconversion-5.c: New test.
* g++.dg/Wconversion3.C: New test.
2007-11-23 Richard Guenther <rguenther@suse.de>
* gcc.dg/tree-ssa/alias-17.c: New testcase.

35
gcc/testsuite/g++.dg/warn/Wconversion3.C Normal file
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@ -0,0 +1,35 @@
// PR c++/34198
// { dg-do compile }
// { dg-options "-O2 -Wconversion -Wsign-conversion" }
signed char sc;
unsigned char uc;
short int ss;
unsigned short int us;
int si;
unsigned int ui;
void test1 (void)
{
int a = uc & 0xff;
int b = sc & 0x7f;
int c = 0xff & uc;
int d = 0x7f & sc;
int e = uc & sc;
unsigned char f = (int) uc;
signed char g = (int) sc;
unsigned char h = (unsigned int) (short int) uc;
signed char i = (int) (unsigned short int) sc; // { dg-warning "may alter its value" }
unsigned char j = (unsigned int) (short int) us; // { dg-warning "may alter its value" }
signed char k = (int) (unsigned short int) ss; // { dg-warning "may alter its value" }
}
void test2 (void)
{
signed char a = (unsigned char) sc; // { dg-warning "may change the sign" }
unsigned char b = (signed char) uc; // { dg-warning "may change the sign" }
signed char c = (int) (unsigned char) sc; // { dg-warning "may change the sign" }
unsigned char d = (int) (signed char) uc; // { dg-warning "may change the sign" }
int e = (unsigned int) si; // { dg-warning "may change the sign" }
unsigned int f = (int) ui; // { dg-warning "may change the sign" }
}

35
gcc/testsuite/gcc.dg/Wconversion-5.c Normal file
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@ -0,0 +1,35 @@
/* PR c++/34198 */
/* { dg-do compile } */
/* { dg-options "-O2 -Wconversion" } */
signed char sc;
unsigned char uc;
short int ss;
unsigned short int us;
int si;
unsigned int ui;
void test1 (void)
{
int a = uc & 0xff;
int b = sc & 0x7f;
int c = 0xff & uc;
int d = 0x7f & sc;
int e = uc & sc;
unsigned char f = (int) uc;
signed char g = (int) sc;
unsigned char h = (unsigned int) (short int) uc;
signed char i = (int) (unsigned short int) sc; /* { dg-warning "may alter its value" } */
unsigned char j = (unsigned int) (short int) us; /* { dg-warning "may alter its value" } */
signed char k = (int) (unsigned short int) ss; /* { dg-warning "may alter its value" } */
}
void test2 (void)
{
signed char a = (unsigned char) sc; /* { dg-warning "may change the sign" } */
unsigned char b = (signed char) uc; /* { dg-warning "may change the sign" } */
signed char c = (int) (unsigned char) sc; /* { dg-warning "may change the sign" } */
unsigned char d = (int) (signed char) uc; /* { dg-warning "may change the sign" } */
int e = (unsigned int) si; /* { dg-warning "may change the sign" } */
unsigned int f = (int) ui; /* { dg-warning "may change the sign" } */
}