[gcc r13-6551] LRA: For clobbered regs use operand mode instead of the biggest mode

[Vladimir Makarov <vmakarov@gcc.gnu.org>]

https://gcc.gnu.org/g:a6457974a1f443ab58d2334c02260299616c78b8

commit r13-6551-ga6457974a1f443ab58d2334c02260299616c78b8
Author: Vladimir N. Makarov <vmakarov@redhat.com>
Date:   Thu Mar 9 08:41:09 2023 -0500

    LRA: For clobbered regs use operand mode instead of the biggest mode
    
    LRA is too conservative in calculation of conflicts with clobbered regs by
    using the biggest access mode.  This results in failure of possible reg
    coalescing and worse code.  This patch solves the problem.
    
            PR rtl-optimization/108999
    
    gcc/ChangeLog:
    
            * lra-constraints.cc (process_alt_operands): Use operand modes for
            clobbered regs instead of the biggest access mode.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.target/aarch64/pr108999.c: New.

Diff:
---
 gcc/lra-constraints.cc                      |  3 ++-
 gcc/testsuite/gcc.target/aarch64/pr108999.c | 21 +++++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index dbfaf0485a5..c38566a7451 100644
--- a/gcc/lra-constraints.cc
+++ b/gcc/lra-constraints.cc
@@ -3108,7 +3108,8 @@ process_alt_operands (int only_alternative)
 	  lra_assert (operand_reg[i] != NULL_RTX);
 	  clobbered_hard_regno = hard_regno[i];
 	  CLEAR_HARD_REG_SET (temp_set);
-	  add_to_hard_reg_set (&temp_set, biggest_mode[i], clobbered_hard_regno);
+	  add_to_hard_reg_set (&temp_set, GET_MODE (*curr_id->operand_loc[i]),
+			       clobbered_hard_regno);
 	  first_conflict_j = last_conflict_j = -1;
 	  for (j = 0; j < n_operands; j++)
 	    if (j == i
diff --git a/gcc/testsuite/gcc.target/aarch64/pr108999.c b/gcc/testsuite/gcc.target/aarch64/pr108999.c
new file mode 100644
index 00000000000..a34db85be83
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr108999.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -march=armv8.2-a+sve" } */
+#include <arm_sve.h>
+
+void subreg_coalesce5 (
+    svbool_t pg, int64_t* base, int n,
+    int64_t *in1, int64_t *in2, int64_t*out
+)
+{
+    svint64x2_t result = svld2_s64 (pg, base);
+
+    for (int i = 0; i < n; i += 1) {
+        svint64_t v18 = svld1_s64(pg, in1 + i);
+        svint64_t v19 = svld1_s64(pg, in2 + i);
+        result.__val[0] = svmad_s64_z(pg, v18, v19, result.__val[0]);
+        result.__val[1] = svmad_s64_z(pg, v18, v19, result.__val[1]);
+    }
+    svst2_s64(pg, out, result);
+}
+
+/* { dg-final { scan-assembler-not {[ \t]*mov[ \t]*z[0-9]+\.d} } } */