https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96536
--- Comment #6 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Hongtao.liu from comment #1)
> I'm testing patch like
>
> emit_insn ((word_mode == SImode)
> ? gen_incsspsi (reg_255)
> : gen_incsspdi (reg_255));
> - tmp = gen_rtx_SET (reg_adj, gen_rtx_MINUS (ptr_mode,
> - reg_adj,
> - GEN_INT (255)));
> - clob = gen_rtx_CLOBBER (VOIDmode, gen_rtx_REG (CCmode, FLAGS_REG));
> - tmp = gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, tmp, clob));
> - emit_insn (tmp);
> -
> - tmp = gen_rtx_COMPARE (CCmode, reg_adj, GEN_INT (255));
> + emit_insn ((ptr_mode == SImode)
> + ? gen_subsi3 (reg_adj, reg_adj, GEN_INT (255))
> + : gen_subdi3 (reg_adj, reg_adj, GEN_INT (255)));
> + tmp = gen_rtx_COMPARE (CCmode, reg_adj, const0_rtx);
> flags = gen_rtx_REG (CCmode, FLAGS_REG);
> emit_insn (gen_rtx_SET (flags, tmp));
The above part is not correct. The original code compares result with 255, your
patch compares result with 0.
So, the minimum patch (for backport) should just introduce:
--cut here--
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 292de142e90..6c207be3512 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -18695,6 +18695,10 @@
tmp = gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, tmp, clob));
emit_insn (tmp);
+ tmp = gen_rtx_COMPARE (CCZmode, reg_ssp, const0_rtx);
+ flags = gen_rtx_REG (CCZmode, FLAGS_REG);
+ emit_insn (gen_rtx_SET (flags, tmp));
+
/* Compare and jump over adjustment code. */
noadj_label = gen_label_rtx ();
flags = gen_rtx_REG (CCZmode, FLAGS_REG);
--cut here--
The patch creates correct form of sub insn (tested with cet-sjlj-1.c testcase):
#(insn 15 14 16 2 (parallel [
# (set (reg:CCZ 17 flags)
# (compare:CCZ (minus:DI (reg:DI 0 ax [85])
# (mem:DI (const:DI (plus:DI (symbol_ref:DI ("buf")
[flags 0x2] <var_decl 0x7f41c308cb40 buf>)
# (const_int 16 [0x10]))) [2 S8 A8]))
# (const_int 0 [0])))
# (set (reg:DI 0 ax [85])
# (minus:DI (reg:DI 0 ax [85])
# (mem:DI (const:DI (plus:DI (symbol_ref:DI ("buf") [flags
0x2] <var_decl 0x7f41c308cb40 buf>)
# (const_int 16 [0x10]))) [2 S8 A8])))
# ]) "cet-sjlj-1.c":16:3 262 {*subdi_2}
# (nil))
subq buf+16(%rip), %rax # 15 [c=8 l=7] *subdi_2/1
