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

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)

2022-10-24  Jakub Jelinek  <jakub@redhat.com>

	PR c++/107358
gcc/c/
	* c-typeck.cc (build_binary_op): Pass operands before excess precision
	promotions to scalar_to_vector call.
gcc/cp/
	* typeck.cc (cp_build_binary_op): Pass operands before excess precision
	promotions to scalar_to_vector call.
gcc/testsuite/
	* c-c++-common/pr107358.c: New test.
	* g++.dg/cpp1y/pr68180.C: Remove -fexcess-precision=fast from
	dg-options.

4 files changed, 38 insertions, 5 deletions

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index fdb96c2..92f3afc 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -11995,8 +11995,8 @@ build_binary_op (location_t location, enum tree_code code,
   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)
 	{
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 16e7d85..530d260b 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -5191,6 +5191,8 @@ cp_build_binary_op (const op_location_t &location,
 
   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 &location,
   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)
         {
diff --git a/gcc/testsuite/c-c++-common/pr107358.c b/gcc/testsuite/c-c++-common/pr107358.c
new file mode 100644
index 0000000..4ab75e0
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr107358.c
@@ -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;
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/pr68180.C b/gcc/testsuite/g++.dg/cpp1y/pr68180.C
index 64d613e..9e6e5e9 100644
--- a/gcc/testsuite/g++.dg/cpp1y/pr68180.C
+++ b/gcc/testsuite/g++.dg/cpp1y/pr68180.C
@@ -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) {