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How to debug if scheduling in gcc is wrong?
- From: "袁立威" <xzfkiller at gmail dot com>
- To: gcc <gcc at gcc dot gnu dot org>
- Date: Wed, 15 Oct 2008 16:19:45 +0800
- Subject: How to debug if scheduling in gcc is wrong?
Hi, I'm a guy working with gcc4.1.1 on itanium2. In my work, some
instrumentations are added by gcc. After instrumentation, all
specint2000 benchmarks except gzip can successfully run with
optimization flag -O3. There are some information list below:
1. Gzip can successfully run when compile with -O1(-O2 and -O3 failed).
2. When add code "while(1)" in an unreachable place in function
"huft_build", gzip can successfully run.
3. Our instrumentation add two new instruction supports to gcc, which
are tnat and single predicate compare:
Machine description file
===========================================================================================
(define_insn "shift_predicate_cmp"
[(set (match_operand:BI 0 "register_operand" "=c")
(and:BI (and:BI (const_int 1)
(ne:BI (match_operand:DI 1 "gr_reg_or_8bit_adjusted_operand" "rL")
(match_operand:DI 2 "gr_register_operand" "r")))
(const_int 1)))]
""
"cmp.ne %0, p0 = %1, %2"
[(set_attr "itanium_class" "icmp")])
(define_insn "shift_tnat"
[(set (match_operand:BI 0 "register_operand" "=c")
(unspec:BI [(match_operand:DI 1 "gr_register_operand" "r")]
UNSPEC_TNAT))]
""
"tnat.nz %0, p0 = %1"
[(set_attr "itanium_class" "tbit")])
============================================================================================
4. Impossible to compare compiled .s files(the one with "while(1)" vs.
the one without) since instruction scheduling make it completely
different.
My question are:
1. Whether this implementation could possibly make gcc's scheduling go wrong?
2. Is there any good way to debug such problems?
Any help are appreciated, thanks very much.