https://gcc.gnu.org/g:70905bad8ea7e9e5f807b54ad3fe183f643cdbf2
commit r16-1977-g70905bad8ea7e9e5f807b54ad3fe183f643cdbf2
Author: Karl Meakin <karl.mea...@arm.com>
Date: Thu Jul 3 12:48:29 2025 +0100
AArch64: add constants for branch displacements
Extract the hardcoded values for the minimum PC-relative displacements
into named constants and document them.
gcc/ChangeLog:
* config/aarch64/aarch64.md (BRANCH_LEN_P_1MiB): New constant.
(BRANCH_LEN_N_1MiB): Likewise.
(BRANCH_LEN_P_32KiB): Likewise.
(BRANCH_LEN_N_32KiB): Likewise.
Diff:
---
gcc/config/aarch64/aarch64.md | 60 +++++++++++++++++++++++++++++++------------
1 file changed, 44 insertions(+), 16 deletions(-)
diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index 8ce991e2f351..3f37ea6cff7c 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -704,7 +704,19 @@
[(set_attr "type" "branch")]
)
+;; Maximum PC-relative positive/negative displacements for various branching
+;; instructions.
+(define_constants
+ [
+ ;; +/- 1MiB. Used by B.<cond>, CBZ, CBNZ.
+ (BRANCH_LEN_P_1MiB 1048572)
+ (BRANCH_LEN_N_1MiB -1048576)
+ ;; +/- 32KiB. Used by TBZ, TBNZ.
+ (BRANCH_LEN_P_32KiB 32764)
+ (BRANCH_LEN_N_32KiB -32768)
+ ]
+)
;; -------------------------------------------------------------------
;; Conditional jumps
@@ -769,13 +781,17 @@
}
[(set_attr "type" "branch")
(set (attr "length")
- (if_then_else (and (ge (minus (match_dup 2) (pc)) (const_int -1048576))
- (lt (minus (match_dup 2) (pc)) (const_int 1048572)))
+ (if_then_else (and (ge (minus (match_dup 2) (pc))
+ (const_int BRANCH_LEN_N_1MiB))
+ (lt (minus (match_dup 2) (pc))
+ (const_int BRANCH_LEN_P_1MiB)))
(const_int 4)
(const_int 8)))
(set (attr "far_branch")
- (if_then_else (and (ge (minus (match_dup 2) (pc)) (const_int -1048576))
- (lt (minus (match_dup 2) (pc)) (const_int 1048572)))
+ (if_then_else (and (ge (minus (match_dup 2) (pc))
+ (const_int BRANCH_LEN_N_1MiB))
+ (lt (minus (match_dup 2) (pc))
+ (const_int BRANCH_LEN_P_1MiB)))
(const_int 0)
(const_int 1)))]
)
@@ -830,13 +846,17 @@
}
[(set_attr "type" "branch")
(set (attr "length")
- (if_then_else (and (ge (minus (match_dup 1) (pc)) (const_int -1048576))
- (lt (minus (match_dup 1) (pc)) (const_int 1048572)))
+ (if_then_else (and (ge (minus (match_dup 1) (pc))
+ (const_int BRANCH_LEN_N_1MiB))
+ (lt (minus (match_dup 1) (pc))
+ (const_int BRANCH_LEN_P_1MiB)))
(const_int 4)
(const_int 8)))
(set (attr "far_branch")
- (if_then_else (and (ge (minus (match_dup 2) (pc)) (const_int -1048576))
- (lt (minus (match_dup 2) (pc)) (const_int 1048572)))
+ (if_then_else (and (ge (minus (match_dup 2) (pc))
+ (const_int BRANCH_LEN_N_1MiB))
+ (lt (minus (match_dup 2) (pc))
+ (const_int BRANCH_LEN_P_1MiB)))
(const_int 0)
(const_int 1)))]
)
@@ -870,13 +890,17 @@
}
[(set_attr "type" "branch")
(set (attr "length")
- (if_then_else (and (ge (minus (match_dup 1) (pc)) (const_int -32768))
- (lt (minus (match_dup 1) (pc)) (const_int 32764)))
+ (if_then_else (and (ge (minus (match_dup 1) (pc))
+ (const_int BRANCH_LEN_N_32KiB))
+ (lt (minus (match_dup 1) (pc))
+ (const_int BRANCH_LEN_P_32KiB)))
(const_int 4)
(const_int 8)))
(set (attr "far_branch")
- (if_then_else (and (ge (minus (match_dup 1) (pc)) (const_int -1048576))
- (lt (minus (match_dup 1) (pc)) (const_int 1048572)))
+ (if_then_else (and (ge (minus (match_dup 1) (pc))
+ (const_int BRANCH_LEN_N_1MiB))
+ (lt (minus (match_dup 1) (pc))
+ (const_int BRANCH_LEN_P_1MiB)))
(const_int 0)
(const_int 1)))]
)
@@ -931,13 +955,17 @@
}
[(set_attr "type" "branch")
(set (attr "length")
- (if_then_else (and (ge (minus (match_dup 2) (pc)) (const_int -32768))
- (lt (minus (match_dup 2) (pc)) (const_int 32764)))
+ (if_then_else (and (ge (minus (match_dup 2) (pc))
+ (const_int BRANCH_LEN_N_32KiB))
+ (lt (minus (match_dup 2) (pc))
+ (const_int BRANCH_LEN_P_32KiB)))
(const_int 4)
(const_int 8)))
(set (attr "far_branch")
- (if_then_else (and (ge (minus (match_dup 2) (pc)) (const_int -1048576))
- (lt (minus (match_dup 2) (pc)) (const_int 1048572)))
+ (if_then_else (and (ge (minus (match_dup 2) (pc))
+ (const_int BRANCH_LEN_N_1MiB))
+ (lt (minus (match_dup 2) (pc))
+ (const_int BRANCH_LEN_P_1MiB)))
(const_int 0)
(const_int 1)))]
