Re: [PATCH] c, c++: Fix up excess precision handling of scalar_to_vector conversion [PR107358]

[Jason Merrill <jason@redhat.com>]

On 10/24/22 03:19, Jakub Jelinek wrote:
> Hi!
> 
> As mentioned earlier in the C++ excess precision support mail, the following
> testcase is broken with excess precision both in C and C++ (though just in C++
> it was triggered in real-world code).
> scalar_to_vector is called in both FEs after the excess precision promotions
> (or stripping of EXCESS_PRECISION_EXPR), so we can then get invalid
> diagnostics that say float vector + float involves truncation (on ia32
> from long double to float).
> 
> The following patch fixes that by calling scalar_to_vector on the operands
> before the excess precision promotions, let scalar_to_vector just do the
> diagnostics (it does e.g. fold_for_warn so it will fold
> EXCESS_PRECISION_EXPR around REAL_CST to constants etc.) but will then
> do the actual conversions using the excess precision promoted operands
> (so say if we have vector double + (float + float) we don't actually do
> vector double + (float) ((long double) float + (long double) float)
> but
> vector double + (double) ((long double) float + (long double) float)
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK on Wednesday if Joseph doesn't object.

> 2022-10-24  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/107358
> c/
> 	* c-typeck.cc (build_binary_op): Pass operands before excess precision
> 	promotions to scalar_to_vector call.
> cp/
> 	* typeck.cc (cp_build_binary_op): Pass operands before excess precision
> 	promotions to scalar_to_vector call.
> testsuite/
> 	* c-c++-common/pr107358.c: New test.
> 	* g++.dg/cpp1y/pr68180.C: Remove -fexcess-precision=fast from
> 	dg-options.
> 
> --- gcc/c/c-typeck.cc.jj	2022-10-14 09:35:56.199990261 +0200
> +++ gcc/c/c-typeck.cc	2022-10-22 17:54:24.378839301 +0200
> @@ -11995,8 +11995,8 @@ build_binary_op (location_t location, en
>     if ((gnu_vector_type_p (type0) && code1 != VECTOR_TYPE)
>         || (gnu_vector_type_p (type1) && code0 != VECTOR_TYPE))
>       {
> -      enum stv_conv convert_flag = scalar_to_vector (location, code, op0, op1,
> -						     true);
> +      enum stv_conv convert_flag = scalar_to_vector (location, code, orig_op0,
> +						     orig_op1, true);
>   
>         switch (convert_flag)
>   	{
> --- gcc/cp/typeck.cc.jj	2022-10-20 13:54:22.535670240 +0200
> +++ gcc/cp/typeck.cc	2022-10-22 17:56:58.589715301 +0200
> @@ -5191,6 +5191,8 @@ cp_build_binary_op (const op_location_t
>   
>     orig_type0 = type0 = TREE_TYPE (op0);
>     orig_type1 = type1 = TREE_TYPE (op1);
> +  tree non_ep_op0 = op0;
> +  tree non_ep_op1 = op1;
>   
>     /* The expression codes of the data types of the arguments tell us
>        whether the arguments are integers, floating, pointers, etc.  */
> @@ -5303,8 +5305,9 @@ cp_build_binary_op (const op_location_t
>     if ((gnu_vector_type_p (type0) && code1 != VECTOR_TYPE)
>         || (gnu_vector_type_p (type1) && code0 != VECTOR_TYPE))
>       {
> -      enum stv_conv convert_flag = scalar_to_vector (location, code, op0, op1,
> -						     complain & tf_error);
> +      enum stv_conv convert_flag
> +	= scalar_to_vector (location, code, non_ep_op0, non_ep_op1,
> +			    complain & tf_error);
>   
>         switch (convert_flag)
>           {
> --- gcc/testsuite/c-c++-common/pr107358.c.jj	2022-10-22 18:46:59.390375310 +0200
> +++ gcc/testsuite/c-c++-common/pr107358.c	2022-10-22 18:01:52.973660719 +0200
> @@ -0,0 +1,30 @@
> +/* PR c++/107358 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fexcess-precision=standard" } */
> +
> +typedef float __attribute__((vector_size (4 * sizeof (float)))) A;
> +typedef double __attribute__((vector_size (2 * sizeof (double)))) B;
> +
> +void
> +foo (A *x)
> +{
> +  *x = *x - 124.225514990f;
> +}
> +
> +void
> +bar (A *x, float y)
> +{
> +  *x = *x - y;
> +}
> +
> +void
> +baz (B *x)
> +{
> +  *x = *x + 124.225514990f;
> +}
> +
> +void
> +qux (B *x, double y)
> +{
> +  *x = *x + y;
> +}
> --- gcc/testsuite/g++.dg/cpp1y/pr68180.C.jj	2022-10-14 09:28:28.339159477 +0200
> +++ gcc/testsuite/g++.dg/cpp1y/pr68180.C	2022-10-22 17:59:07.012946513 +0200
> @@ -1,6 +1,6 @@
>   // PR c++/68180
>   // { dg-do compile { target c++14 } }
> -// { dg-additional-options "-Wno-psabi -fexcess-precision=fast" }
> +// { dg-additional-options "-Wno-psabi" }
>   
>   typedef float __attribute__( ( vector_size( 16 ) ) ) float32x4_t;
>   constexpr float32x4_t fill(float x) {
> 
> 	Jakub
>