[PATCH v2] varasm: Use native_encode_rtx for constant vectors.

optimize_constant_pool hashes vector masks by native_encode_rtx and
merges identically hashed values in the constant pool.  Afterwards the
optimized values are written in output_constant_pool_2.

However, native_encode_rtx and output_constant_pool_2 disagree in their
encoding of vector masks:  native_encode_rtx does not pad with zeroes
while output_constant_pool_2 implicitly does.

In RVV's shuffle-evenodd-run.c there are two masks
  (a) "0101" for V4BI
  (b) "01010101" for V8BI and
that have the same representation/encoding ("1010101") in native_encode_rtx.
output_constant_pool_2 uses "101" for (a) and "1010101" for (b).

Now, optimize_constant_pool might happen to merge both masks using
(a) as representative.  Then, output_constant_pool_2 will output "1010"
which is only valid for the second mask as the implicit zero padding
doesn't agree with (b).
(b)'s "1010101" works for both masks as a V4BI load will ignore the last four
padding bits.

This patch makes output_constant_pool_2 use native_encode_rtx so both
functions will agree on an encoding and output the correct constant.

	PR target/118036
gcc/ChangeLog:

	* varasm.cc (output_constant_pool_2): Use native_encode_rtx for
	building the memory image of a const vector mask.

1 files changed, 10 insertions, 27 deletions

diff --git a/gcc/varasm.cc b/gcc/varasm.cc
index 0068ec2..507da62 100644
--- a/gcc/varasm.cc
+++ b/gcc/varasm.cc
@@ -4301,34 +4301,17 @@ output_constant_pool_2 (fixed_size_mode mode, rtx x, unsigned int align)
       {
 	gcc_assert (GET_CODE (x) == CONST_VECTOR);
 
-	/* Pick the smallest integer mode that contains at least one
-	   whole element.  Often this is byte_mode and contains more
-	   than one element.  */
-	unsigned int nelts = GET_MODE_NUNITS (mode);
-	unsigned int elt_bits = GET_MODE_PRECISION (mode) / nelts;
-	unsigned int int_bits = MAX (elt_bits, BITS_PER_UNIT);
-	scalar_int_mode int_mode = int_mode_for_size (int_bits, 0).require ();
-	unsigned int mask = GET_MODE_MASK (GET_MODE_INNER (mode));
-
-	/* We allow GET_MODE_PRECISION (mode) <= GET_MODE_BITSIZE (mode) but
-	   only properly handle cases where the difference is less than a
-	   byte.  */
-	gcc_assert (GET_MODE_BITSIZE (mode) - GET_MODE_PRECISION (mode) <
-		    BITS_PER_UNIT);
-
-	/* Build the constant up one integer at a time.  */
-	unsigned int elts_per_int = int_bits / elt_bits;
-	for (unsigned int i = 0; i < nelts; i += elts_per_int)
+	auto_vec<target_unit, 128> buffer;
+	buffer.reserve (GET_MODE_SIZE (mode));
+
+	bool ok = native_encode_rtx (mode, x, buffer, 0, GET_MODE_SIZE (mode));
+	gcc_assert (ok);
+
+	for (unsigned i = 0; i < GET_MODE_SIZE (mode); i++)
 	  {
-	    unsigned HOST_WIDE_INT value = 0;
-	    unsigned int limit = MIN (nelts - i, elts_per_int);
-	    for (unsigned int j = 0; j < limit; ++j)
-	    {
-	      auto elt = INTVAL (CONST_VECTOR_ELT (x, i + j));
-	      value |= (elt & mask) << (j * elt_bits);
-	    }
-	    output_constant_pool_2 (int_mode, gen_int_mode (value, int_mode),
-				    i != 0 ? MIN (align, int_bits) : align);
+	    unsigned HOST_WIDE_INT value = buffer[i];
+	    output_constant_pool_2 (byte_mode, gen_int_mode (value, byte_mode),
+				    i == 0 ? align : 1);
 	  }
 	break;
       }