This is the mail archive of the
gcc-bugs@gcc.gnu.org
mailing list for the GCC project.
[Bug target/64154] enable fipa-ra for Thumb1
- From: "vries at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 08 Jan 2015 13:55:50 +0000
- Subject: [Bug target/64154] enable fipa-ra for Thumb1
- Auto-submitted: auto-generated
- References: <bug-64154-4 at http dot gcc dot gnu dot org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64154
--- Comment #3 from vries at gcc dot gnu.org ---
(In reply to Terry Guo from comment #2)
> Hi Tom,
>
> I enabled this optimization to thumb1 target cortex-m0
Does that mean you just reverted the patch for PR63718?
> and found this IPA-RA
> optimization doesn't consider the register clobber information attached to
> call rtx
The IPA-RA analysis does consider that clobber. It's using
find_all_hard_reg_sets, and that function contains a loop over
CALL_INSN_FUNCTION_USAGE.
> and thus generated bad code. Here are the bad rtxs I extracted from
> the dump of cprop_hardreg pass:
>
> (insn 292 291 141 13 (set (reg:SI 4 r4 [orig:163 ivtmp.108 ] [163])
> (reg:SI 12 ip [orig:163 ivtmp.108 ] [163])) 742 {*thumb1_movsi_insn}
> (expr_list:REG_DEAD (reg:SI 12 ip [orig:163 ivtmp.108 ] [163])
> (nil)))
>
> (call_insn 141 292 142 13 (parallel [
> (call (mem:SI (symbol_ref:SI ("f2") [flags 0x3] <function_decl
> 0x7f8182689100 f2>) [0 f2 S4 A32])
> (const_int 0 [0]))
> (use (const_int 0 [0]))
> (clobber (reg:SI 14 lr))
> ])
> /myssd/terguo01/toolchain-build/GCC32RM-424/src/gcc/gcc/testsuite/gcc.dg/
> vshift-3.c:119 770 {*call_insn}
> (expr_list:REG_CALL_DECL (symbol_ref:SI ("f2") [flags 0x3]
> <function_decl 0x7f8182689100 f2>)
> (expr_list:REG_EH_REGION (const_int 0 [0])
> (nil)))
> (expr_list (clobber (reg:SI 12 ip))
> (nil)))
>
> (insn 11 10 12 13 (set (reg:SI 0 r0 [orig:170 ivtmp.130 ] [170])
> (reg:SI 12 ip [orig:163 ivtmp.108 ] [163]))
> /myssd/terguo01/toolchain-build/GCC32RM-424/src/gcc/gcc/testsuite/gcc.dg/
> vshift-3.c:121 742 {*thumb1_movsi_insn}
> (expr_list:REG_EQUAL (symbol_ref:SI ("j") [flags 0x80] <var_decl
> 0x7f81827d0750 j>)
> (nil)))
>
That is wrong indeed: ip is explicitly clobbered by the call in
CALL_INSN_FUNCTION_USAGE, but used as if not clobbered by the call.
> I checked the code in 'if (CALL_P (insn))' part in file regcprop.c and found
> the algorithm doesn't consider the '(expr_list (clobber (reg:SI 12 ip))' in
> insn 141 which makes current algorithm think it is safe to propagate ip from
> insn 292 to insn 11.
>
I cannot reproduce the wrong code as listed above. But I can reproduce the
clobber being skipped by copyprop_hardreg_forward_1. So I agree, cprop_hardreg
does not respect the clobber on the call in CALL_INSN_FUNCTION_USAGE.
I'll file a PR.