[gcc r11-8904] arm: fix vlldm erratum for Armv8.1-m [PR102035]

[Richard Earnshaw <rearnsha@gcc.gnu.org>]

https://gcc.gnu.org/g:8933c1b66a6b7a66b8843e21c8cb6c0679fc2d09

commit r11-8904-g8933c1b66a6b7a66b8843e21c8cb6c0679fc2d09
Author: Richard Earnshaw <rearnsha@arm.com>
Date:   Fri Jun 18 17:18:37 2021 +0100

    arm: fix vlldm erratum for Armv8.1-m [PR102035]
    
    For Armv8.1-m we generate code that emits VLLDM directly and do not
    rely on support code in the library, so emit the mitigation directly
    as well, when required.  In this case, we can use the compiler options
    to determine when to apply the fix and when it is safe to omit it.
    
    gcc:
            PR target/102035
            * config/arm/arm.md (attribute arch): Add fix_vlldm.
            (arch_enabled): Use it.
            * config/arm/vfp.md (lazy_store_multiple_insn): Add alternative to
            use when erratum mitigation is needed.
    (cherry picked from commit 30461cf8dba3d3adb15a125e4da48800eb2b9b8f)

Diff:
---
 gcc/config/arm/arm.md | 11 +++++++++--
 gcc/config/arm/vfp.md | 10 +++++++---
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index 064604808cc..5d3f21b91c4 100644
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -132,9 +132,12 @@
 ; TARGET_32BIT, "t1" or "t2" to specify a specific Thumb mode.  "v6"
 ; for ARM or Thumb-2 with arm_arch6, and nov6 for ARM without
 ; arm_arch6.  "v6t2" for Thumb-2 with arm_arch6 and "v8mb" for ARMv8-M
-; Baseline.  This attribute is used to compute attribute "enabled",
+; Baseline.  "fix_vlldm" is for fixing the v8-m/v8.1-m VLLDM erratum.
+; This attribute is used to compute attribute "enabled",
 ; use type "any" to enable an alternative in all cases.
-(define_attr "arch" "any,a,t,32,t1,t2,v6,nov6,v6t2,v8mb,iwmmxt,iwmmxt2,armv6_or_vfpv3,neon,mve"
+(define_attr "arch" "any, a, t, 32, t1, t2, v6,nov6, v6t2, \
+		     v8mb, fix_vlldm, iwmmxt, iwmmxt2, armv6_or_vfpv3, \
+		     neon, mve"
   (const_string "any"))
 
 (define_attr "arch_enabled" "no,yes"
@@ -177,6 +180,10 @@
 	      (match_test "TARGET_THUMB1 && arm_arch8"))
 	 (const_string "yes")
 
+	 (and (eq_attr "arch" "fix_vlldm")
+	      (match_test "fix_vlldm"))
+	 (const_string "yes")
+
 	 (and (eq_attr "arch" "iwmmxt2")
 	      (match_test "TARGET_REALLY_IWMMXT2"))
 	 (const_string "yes")
diff --git a/gcc/config/arm/vfp.md b/gcc/config/arm/vfp.md
index 6cf5a5d8b69..c9f2f12b51e 100644
--- a/gcc/config/arm/vfp.md
+++ b/gcc/config/arm/vfp.md
@@ -1720,11 +1720,15 @@
 
 (define_insn "lazy_load_multiple_insn"
   [(unspec_volatile
-    [(mem:BLK (match_operand:SI 0 "s_register_operand" "rk"))]
+    [(mem:BLK (match_operand:SI 0 "s_register_operand" "rk,rk"))]
     VUNSPEC_VLLDM)]
   "use_cmse && reload_completed"
-  "vlldm%?\\t%0"
-  [(set_attr "predicable" "yes")
+  "@
+   vscclrm\\t{vpr}\;vlldm\\t%0
+   vlldm\\t%0"
+  [(set_attr "arch" "fix_vlldm,*")
+   (set_attr "predicable" "no")
+   (set_attr "length" "8,4")
    (set_attr "type" "load_4")]
 )