https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69713
--- Comment #5 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Oleg Endo from comment #4)
>
> Option 3)
> Try adding a T_REG use in casesi_worker_0/casesi_worker_1 patterns to create
> a link between the bounds checking insn and the table access insns.
>
The following patch does that. It seems to work for the test case of this PR.
However, it relies on the fact that the problematic transformations are done
before register allocation. If some similar optimizations are done after
register allocation (in the future) this probably will break again.
Anyway, I think this could be applied to GCC 5 and GCC 6. Kaz, what do you
think?
Index: gcc/config/sh/sh.md
===================================================================
--- gcc/config/sh/sh.md (revision 233200)
+++ gcc/config/sh/sh.md (working copy)
@@ -11707,12 +11707,16 @@
;; ??? reload might clobber r0 if we use it explicitly in the RTL before
;; reload; using a R0_REGS pseudo reg is likely to give poor code.
;; So we keep the use of r0 hidden in a R0_REGS clobber until after reload.
+;;
+;; The use on the T_REG in the casesi_worker* patterns links the bounds
+;; checking insns and the table memory access. See also PR 69713.
(define_insn "casesi_worker_0"
[(set (match_operand:SI 0 "register_operand" "=r,r")
(unspec:SI [(match_operand:SI 1 "register_operand" "0,r")
(label_ref (match_operand 2 "" ""))] UNSPEC_CASESI))
(clobber (match_scratch:SI 3 "=X,1"))
- (clobber (match_scratch:SI 4 "=&z,z"))]
+ (clobber (match_scratch:SI 4 "=&z,z"))
+ (use (reg:SI T_REG))]
"TARGET_SH1"
"#")
@@ -11721,7 +11725,8 @@
(unspec:SI [(match_operand:SI 1 "register_operand" "")
(label_ref (match_operand 2 "" ""))] UNSPEC_CASESI))
(clobber (match_scratch:SI 3 ""))
- (clobber (match_scratch:SI 4 ""))]
+ (clobber (match_scratch:SI 4))
+ (use (reg:SI T_REG))]
"TARGET_SH1 && ! TARGET_SH2 && reload_completed"
[(set (reg:SI R0_REG) (unspec:SI [(label_ref (match_dup 2))] UNSPEC_MOVA))
(parallel [(set (match_dup 0)
@@ -11739,7 +11744,8 @@
(unspec:SI [(match_operand:SI 1 "register_operand" "")
(label_ref (match_operand 2 "" ""))] UNSPEC_CASESI))
(clobber (match_scratch:SI 3 ""))
- (clobber (match_scratch:SI 4 ""))]
+ (clobber (match_scratch:SI 4))
+ (use (reg:SI T_REG))]
"TARGET_SH2 && reload_completed"
[(set (reg:SI R0_REG) (unspec:SI [(label_ref (match_dup 2))] UNSPEC_MOVA))
(parallel [(set (match_dup 0)
