From db4e496aadf1d7ab1c5af24410394d1551ddd3f0 Mon Sep 17 00:00:00 2001
From: Wilco Dijkstra <wilco.dijkstra@arm.com>
Date: Tue, 16 Jan 2024 16:27:02 +0000
Subject: [PATCH] AArch64: Reassociate CONST in address expressions

GCC tends to optimistically create CONST of globals with an immediate offset.
However it is almost always better to CSE addresses of globals and add immediate
offsets separately (the offset could be merged later in single-use cases).
Splitting CONST expressions with an index in aarch64_legitimize_address fixes
part of PR112573.

gcc/ChangeLog:
	PR target/112573
	* config/aarch64/aarch64.cc (aarch64_legitimize_address): Reassociate
	badly formed CONST expressions.

gcc/testsuite/ChangeLog:
	PR target/112573
	* gcc.target/aarch64/pr112573.c: Add new test.
---
 gcc/config/aarch64/aarch64.cc               | 11 +++++++++++
 gcc/testsuite/gcc.target/aarch64/pr112573.c | 15 +++++++++++++++
 2 files changed, 26 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/aarch64/pr112573.c

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 7d1f8c65ce41..e6bd3fd0bb42 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -12617,6 +12617,17 @@ aarch64_legitimize_address (rtx x, rtx /* orig_x  */, machine_mode mode)
      not to split a CONST for some forms of address expression, otherwise
      it will generate sub-optimal code.  */
 
+  /* First split X + CONST (base, offset) into (base + X) + offset.  */
+  if (GET_CODE (x) == PLUS && GET_CODE (XEXP (x, 1)) == CONST)
+    {
+      poly_int64 offset;
+      rtx base = strip_offset (XEXP (x, 1), &offset);
+
+      base = expand_binop (Pmode, add_optab, base, XEXP (x, 0),
+			   NULL_RTX, true, OPTAB_DIRECT);
+      x = plus_constant (Pmode, base, offset);
+    }
+
   if (GET_CODE (x) == PLUS && CONST_INT_P (XEXP (x, 1)))
     {
       rtx base = XEXP (x, 0);
diff --git a/gcc/testsuite/gcc.target/aarch64/pr112573.c b/gcc/testsuite/gcc.target/aarch64/pr112573.c
new file mode 100644
index 000000000000..be04c0ca86ad
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr112573.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-section-anchors" } */
+
+char a[100];
+
+void f1 (int x, int y)
+{
+  *((a + y) + 3) = x;
+  *((a + y) + 2) = x;
+  *((a + y) + 1) = x;
+  *((a + y) + 0) = x;
+}
+
+/* { dg-final { scan-assembler-times "strb" 4 } } */
+/* { dg-final { scan-assembler-times "adrp" 1 } } */
-- 
2.47.2