c-family: Fix up -W*conversion on bitwise &/|/^ [PR101537]

Hi!

The following testcases emit a bogus -Wconversion warning.  This is because
conversion_warning function doesn't handle BIT_*_EXPR (only unsafe_conversion_p
that is called during the default: case, and that one doesn't handle
SAVE_EXPRs added because the unsigned char & or | operands promoted to int
have side-effects and =| or =& is used.

The patch handles BIT_IOR_EXPR/BIT_XOR_EXPR like the last 2 operands of
COND_EXPR by recursing on the two operands, if either of them doesn't fit
into the narrower type, complain.  BIT_AND_EXPR too, but first it needs to
handle some special cases that unsafe_conversion_p does, namely when one
of the two operands is a constant.

This fixes completely the pr101537.c test and for C also pr103881.c
and doesn't regress anything in the testsuite, for C++ pr103881.c still
emits the bogus warnings.
This is because while the C FE emits in that case a SAVE_EXPR that
conversion_warning can handle already, C++ FE emits
TARGET_EXPR <D.whatever, ...>, something | D.whatever
etc. and conversion_warning handles COMPOUND_EXPR by "recursing" on the
rhs.  To handle that case, we'd need for TARGET_EXPR on the lhs remember
in some hash map the mapping from D.whatever to the TARGET_EXPR and when
we see D.whatever, use corresponding TARGET_EXPR initializer instead.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2022-01-04  Jakub Jelinek  <jakub@redhat.com>

	PR c/101537
	PR c/103881
gcc/c-family/
	* c-warn.c (conversion_warning): Handle BIT_AND_EXPR, BIT_IOR_EXPR
	and BIT_XOR_EXPR.
gcc/testsuite/
	* c-c++-common/pr101537.c: New test.
	* c-c++-common/pr103881.c: New test.


	Jakub

On 1/4/22 04:32, Jakub Jelinek wrote:
> Hi!
> 
> The following testcases emit a bogus -Wconversion warning.  This is because
> conversion_warning function doesn't handle BIT_*_EXPR (only unsafe_conversion_p
> that is called during the default: case, and that one doesn't handle
> SAVE_EXPRs added because the unsigned char & or | operands promoted to int
> have side-effects and =| or =& is used.
> 
> The patch handles BIT_IOR_EXPR/BIT_XOR_EXPR like the last 2 operands of
> COND_EXPR by recursing on the two operands, if either of them doesn't fit
> into the narrower type, complain.  BIT_AND_EXPR too, but first it needs to
> handle some special cases that unsafe_conversion_p does, namely when one
> of the two operands is a constant.
> 
> This fixes completely the pr101537.c test and for C also pr103881.c
> and doesn't regress anything in the testsuite, for C++ pr103881.c still
> emits the bogus warnings.
> This is because while the C FE emits in that case a SAVE_EXPR that
> conversion_warning can handle already, C++ FE emits
> TARGET_EXPR <D.whatever, ...>, something | D.whatever

in stabilize_expr, yes.

> etc. and conversion_warning handles COMPOUND_EXPR by "recursing" on the
> rhs.  To handle that case, we'd need for TARGET_EXPR on the lhs remember
> in some hash map the mapping from D.whatever to the TARGET_EXPR and when
> we see D.whatever, use corresponding TARGET_EXPR initializer instead.

Agreed.

> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

> 2022-01-04  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c/101537
> 	PR c/103881
> gcc/c-family/
> 	* c-warn.c (conversion_warning): Handle BIT_AND_EXPR, BIT_IOR_EXPR
> 	and BIT_XOR_EXPR.
> gcc/testsuite/
> 	* c-c++-common/pr101537.c: New test.
> 	* c-c++-common/pr103881.c: New test.
> 
> --- gcc/c-family/c-warn.c.jj	2022-01-03 10:40:49.745044771 +0100
> +++ gcc/c-family/c-warn.c	2022-01-03 12:42:55.174012944 +0100
> @@ -1304,6 +1304,34 @@ conversion_warning (location_t loc, tree
>   		|| conversion_warning (loc, type, op2, result));
>         }
>   
> +    case BIT_AND_EXPR:
> +      if (TREE_CODE (expr_type) == INTEGER_TYPE
> +	  && TREE_CODE (type) == INTEGER_TYPE)
> +	for (int i = 0; i < 2; ++i)
> +	  {
> +	    tree op = TREE_OPERAND (expr, i);
> +	    if (TREE_CODE (op) != INTEGER_CST)
> +	      continue;
> +
> +	    /* If one of the operands is a non-negative constant
> +	       that fits in the target type, then the type of the
> +	       other operand does not matter.  */
> +	    if (int_fits_type_p (op, c_common_signed_type (type))
> +		&& int_fits_type_p (op, c_common_unsigned_type (type)))
> +	      return false;
> +
> +	    /* If constant is unsigned and fits in the target
> +	       type, then the result will also fit.  */
> +	    if (TYPE_UNSIGNED (TREE_TYPE (op)) && int_fits_type_p (op, type))
> +	      return false;
> +	  }
> +      /* FALLTHRU */
> +    case BIT_IOR_EXPR:
> +    case BIT_XOR_EXPR:
> +      return (conversion_warning (loc, type, TREE_OPERAND (expr, 0), result)
> +	      || conversion_warning (loc, type, TREE_OPERAND (expr, 1),
> +				     result));
> +
>       default_:
>       default:
>         conversion_kind = unsafe_conversion_p (type, expr, result, true);
> --- gcc/testsuite/c-c++-common/pr101537.c.jj	2022-01-03 12:08:33.781823852 +0100
> +++ gcc/testsuite/c-c++-common/pr101537.c	2022-01-03 12:08:33.781823852 +0100
> @@ -0,0 +1,26 @@
> +/* PR c/101537 */
> +/* { dg-do compile } */
> +/* { dg-options "-Wconversion" } */
> +
> +int
> +foo ()
> +{
> +  int aaa = 1;
> +  unsigned char bbb = 0;
> +  bbb |= aaa ? 1 : 0;
> +  return bbb;
> +}
> +
> +int
> +bar (unsigned char x, int f)
> +{
> +  x |= f ? 1 : 0;
> +  return x;
> +}
> +
> +int
> +baz (unsigned char x, int f)
> +{
> +  x = x | f ? 1 : 0;
> +  return x;
> +}
> --- gcc/testsuite/c-c++-common/pr103881.c.jj	2022-01-03 12:08:33.781823852 +0100
> +++ gcc/testsuite/c-c++-common/pr103881.c	2022-01-03 12:08:33.781823852 +0100
> @@ -0,0 +1,20 @@
> +/* PR c/103881 */
> +/* { dg-do compile } */
> +/* { dg-options "-Wconversion" } */
> +
> +unsigned char bar (void);
> +
> +void
> +foo (void)
> +{
> +  unsigned char t = 0;
> +  t |= bar ();
> +  t |= bar () & bar ();	/* { dg-bogus "conversion from 'int' to 'unsigned char' may change value" "" { xfail c++ } } */
> +  t &= bar () & bar ();	/* { dg-bogus "conversion from 'int' to 'unsigned char' may change value" "" { xfail c++ } } */
> +  t = bar () & bar ();
> +
> +  unsigned char a = bar ();
> +  t |= a & a;
> +  t |= bar () & a;		/* { dg-bogus "conversion from 'int' to 'unsigned char' may change value" "" { xfail c++ } } */
> +  t |= a & bar ();		/* { dg-bogus "conversion from 'int' to 'unsigned char' may change value" "" { xfail c++ } } */
> +}
> 
> 	Jakub
>