[gcc r13-6410] Avoid creating (const (reg ...)) [PR108603]

[Richard Sandiford <rsandifo@gcc.gnu.org>]

https://gcc.gnu.org/g:b09dc74801cf4e19bdf5fcd18a5cd53fc9e9ca9a

commit r13-6410-gb09dc74801cf4e19bdf5fcd18a5cd53fc9e9ca9a
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Thu Mar 2 10:30:21 2023 +0000

    Avoid creating (const (reg ...)) [PR108603]
    
    convert_memory_address_addr_space_1 has two modes: one in which it
    tries to create a self-contained RTL expression (which might fail)
    and one in which it can emit new instructions where necessary.
    
    When handling a CONST, the function recurses into the CONST's
    operand and then constifies the result.  But that's only valid if
    the result is still a self-contained expression.  If new instructions
    have been emitted, the expression will refer to the (non-constant)
    results of those instructions.
    
    In the PR, this caused us to emit a nonsensical (const (reg ...))
    REG_EQUAL note.
    
    gcc/
            PR tree-optimization/108603
            * explow.cc (convert_memory_address_addr_space_1): Only wrap
            the result of a recursive call in a CONST if no instructions
            were emitted.
    
    gcc/testsuite/
            PR tree-optimization/108603
            * gcc.target/aarch64/sve/pr108603.c: New test.

Diff:
---
 gcc/explow.cc                                   | 11 ++++++++---
 gcc/testsuite/gcc.target/aarch64/sve/pr108603.c |  8 ++++++++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/gcc/explow.cc b/gcc/explow.cc
index 83439b32abe..32e9498ee07 100644
--- a/gcc/explow.cc
+++ b/gcc/explow.cc
@@ -349,9 +349,14 @@ convert_memory_address_addr_space_1 (scalar_int_mode to_mode ATTRIBUTE_UNUSED,
       return temp;
 
     case CONST:
-      temp = convert_memory_address_addr_space_1 (to_mode, XEXP (x, 0), as,
-						  true, no_emit);
-      return temp ? gen_rtx_CONST (to_mode, temp) : temp;
+      {
+	auto *last = no_emit ? nullptr : get_last_insn ();
+	temp = convert_memory_address_addr_space_1 (to_mode, XEXP (x, 0), as,
+						    true, no_emit);
+	if (temp && (no_emit || last == get_last_insn ()))
+	  return gen_rtx_CONST (to_mode, temp);
+	return temp;
+      }
 
     case PLUS:
     case MULT:
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/pr108603.c b/gcc/testsuite/gcc.target/aarch64/sve/pr108603.c
new file mode 100644
index 00000000000..a2aea9f0b12
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/pr108603.c
@@ -0,0 +1,8 @@
+/* { dg-options "-O2 -mabi=ilp32 -fdata-sections" } */
+
+int a[128];
+long long *p;
+void f() {
+  for (long i = 0; i < sizeof(long); i++)
+    p[i] = a[i];
+}