From: Richard Sandiford <richard.sandiford@arm.com>
Date: Tue, 17 Oct 2023 22:46:33 +0000 (+0100)
Subject: aarch64: Put LR save slot first in more cases
X-Git-Tag: basepoints/gcc-15~5441
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=773306e9ef4ea1407f89686eb513a50602493666;p=thirdparty%2Fgcc.git

aarch64: Put LR save slot first in more cases

Now that the prologue and epilogue code iterates over saved
registers in offset order, we can put the LR save slot first
without compromising LDP/STP formation.

This isn't worthwhile when shadow call stacks are enabled, since the
first two registers are also push/pop candidates, and LR cannot be
popped when shadow call stacks are enabled.  (LR is instead loaded
first and compared against the shadow stack's value.)

But otherwise, it seems better to put the LR save slot first,
to reduce unnecessary variation with the layout for stack clash
protection.

gcc/
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Don't make
	the position of the LR save slot dependent on stack clash
	protection unless shadow call stacks are enabled.

gcc/testsuite/
	* gcc.target/aarch64/test_frame_2.c: Expect x30 to come before x19.
	* gcc.target/aarch64/test_frame_4.c: Likewise.
	* gcc.target/aarch64/test_frame_7.c: Likewise.
	* gcc.target/aarch64/test_frame_10.c: Likewise.
---

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index e8b5dfe4d584..62b1ae0652f4 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8694,7 +8694,7 @@ aarch64_layout_frame (void)
       allocate_gpr_slot (R29_REGNUM);
       allocate_gpr_slot (R30_REGNUM);
     }
-  else if (flag_stack_clash_protection
+  else if ((flag_stack_clash_protection || !frame.is_scs_enabled)
 	   && known_eq (frame.reg_offset[R30_REGNUM], SLOT_REQUIRED))
     /* Put the LR save slot first, since it makes a good choice of probe
        for stack clash purposes.  The idea is that the link register usually
diff --git a/gcc/testsuite/gcc.target/aarch64/test_frame_10.c b/gcc/testsuite/gcc.target/aarch64/test_frame_10.c
index c19505082fa1..c54ab2d0ccb4 100644
--- a/gcc/testsuite/gcc.target/aarch64/test_frame_10.c
+++ b/gcc/testsuite/gcc.target/aarch64/test_frame_10.c
@@ -14,6 +14,6 @@
 t_frame_pattern_outgoing (test10, 480, "x19", 24, a[8], a[9], a[10])
 t_frame_run (test10)
 
-/* { dg-final { scan-assembler-times "stp\tx19, x30, \\\[sp, \[0-9\]+\\\]" 1 } } */
-/* { dg-final { scan-assembler "ldp\tx19, x30, \\\[sp, \[0-9\]+\\\]" } } */
+/* { dg-final { scan-assembler-times "stp\tx30, x19, \\\[sp, \[0-9\]+\\\]" 1 } } */
+/* { dg-final { scan-assembler "ldp\tx30, x19, \\\[sp, \[0-9\]+\\\]" } } */
 
diff --git a/gcc/testsuite/gcc.target/aarch64/test_frame_2.c b/gcc/testsuite/gcc.target/aarch64/test_frame_2.c
index 7e5df84cf5f9..0d715314cb83 100644
--- a/gcc/testsuite/gcc.target/aarch64/test_frame_2.c
+++ b/gcc/testsuite/gcc.target/aarch64/test_frame_2.c
@@ -14,6 +14,6 @@ t_frame_pattern (test2, 200, "x19")
 t_frame_run (test2)
 
 
-/* { dg-final { scan-assembler-times "stp\tx19, x30, \\\[sp, -\[0-9\]+\\\]!" 1 } } */
-/* { dg-final { scan-assembler "ldp\tx19, x30, \\\[sp\\\], \[0-9\]+" } } */
+/* { dg-final { scan-assembler-times "stp\tx30, x19, \\\[sp, -\[0-9\]+\\\]!" 1 } } */
+/* { dg-final { scan-assembler "ldp\tx30, x19, \\\[sp\\\], \[0-9\]+" } } */
 
diff --git a/gcc/testsuite/gcc.target/aarch64/test_frame_4.c b/gcc/testsuite/gcc.target/aarch64/test_frame_4.c
index ed13487a094a..b41229c42f45 100644
--- a/gcc/testsuite/gcc.target/aarch64/test_frame_4.c
+++ b/gcc/testsuite/gcc.target/aarch64/test_frame_4.c
@@ -13,6 +13,6 @@
 t_frame_pattern (test4, 400, "x19")
 t_frame_run (test4)
 
-/* { dg-final { scan-assembler-times "stp\tx19, x30, \\\[sp, -\[0-9\]+\\\]!" 1 } } */
-/* { dg-final { scan-assembler "ldp\tx19, x30, \\\[sp\\\], \[0-9\]+" } } */
+/* { dg-final { scan-assembler-times "stp\tx30, x19, \\\[sp, -\[0-9\]+\\\]!" 1 } } */
+/* { dg-final { scan-assembler "ldp\tx30, x19, \\\[sp\\\], \[0-9\]+" } } */
 
diff --git a/gcc/testsuite/gcc.target/aarch64/test_frame_7.c b/gcc/testsuite/gcc.target/aarch64/test_frame_7.c
index 96452794956f..5702656a5da7 100644
--- a/gcc/testsuite/gcc.target/aarch64/test_frame_7.c
+++ b/gcc/testsuite/gcc.target/aarch64/test_frame_7.c
@@ -13,6 +13,6 @@
 t_frame_pattern (test7, 700, "x19")
 t_frame_run (test7)
 
-/* { dg-final { scan-assembler-times "stp\tx19, x30, \\\[sp]" 1 } } */
-/* { dg-final { scan-assembler "ldp\tx19, x30, \\\[sp\\\]" } } */
+/* { dg-final { scan-assembler-times "stp\tx30, x19, \\\[sp]" 1 } } */
+/* { dg-final { scan-assembler "ldp\tx30, x19, \\\[sp\\\]" } } */