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Re: [PATCH] Fix DCE REG_LIBCALL note moving from noop move insns (PR rtl-optimization/33644)
On Fri, Oct 19, 2007 at 11:54:52AM -0400, Jakub Jelinek wrote:
> Anyway, just tried (sorry for the delay) removing the libcall stuff, just
> generate:
> (call_insn/u 5 4 6 mm2.c:4 (parallel [
> (set (reg:DI 0 ax)
> (call:DI (mem:QI (symbol_ref:DI ("__tls_get_addr")) [0 S1 A8])
> (const_int 0 [0x0])))
> (unspec:DI [
> (const_int 0 [0x0])
> ] 20)
> ]) -1 (nil)
> (nil))
>
> (insn 6 5 7 mm2.c:4 (set (reg:DI 60)
> (reg:DI 0 ax)) -1 (nil))
>
> but CSE isn't able to merge these. Will still try to add REG_EQUAL note to
> the pseudo = %rax insn if that helps.
Adding REG_EQUAL note was all that was needed for CSEing it, but dce.c still
won't delete it, because it punts on all UNSPECs. The UNSPECs are really
necessary for the __tls_get_addr call, as the call_insn has mandatory insn
sequence that needs to be output there (to make TLS transitions possible).
The comment says:
/* The UNSPEC case was added here because the ia-64 claims that
USEs do not work after reload and generates UNSPECS rather
than USEs. Since dce is run after reload we need to avoid
deleting these even if they are dead. If it turns out that
USEs really do work after reload, the ia-64 should be
changed, and the UNSPEC case can be removed. */
I wonder what kind of UNSPECs and at what places were the reasons to add it,
I very much doubt not dceing any UNSPECs is desirable, even on ia64.
Say speculative moves use UNSPEC_LDS{,A}, but they certainly should be dced.
--- gcc/config/i386/i386.c.jj 2007-10-19 14:39:55.000000000 +0200
+++ gcc/config/i386/i386.c 2007-10-19 18:05:57.000000000 +0200
@@ -7644,7 +7644,7 @@ legitimize_tls_address (rtx x, enum tls_
if (TARGET_64BIT && ! TARGET_GNU2_TLS)
{
- rtx rax = gen_rtx_REG (Pmode, AX_REG), insns;
+ rtx rax = gen_rtx_REG (Pmode, AX_REG), insns, last;
start_sequence ();
emit_call_insn (gen_tls_global_dynamic_64 (rax, x));
@@ -7652,7 +7652,10 @@ legitimize_tls_address (rtx x, enum tls_
end_sequence ();
CONST_OR_PURE_CALL_P (insns) = 1;
- emit_libcall_block (insns, dest, rax, x);
+/* emit_libcall_block (insns, dest, rax, x); */
+ emit_insn (insns);
+ emit_move_insn (dest, rax);
+ last = set_unique_reg_note (last, REG_EQUAL, x);
}
else if (TARGET_64BIT && TARGET_GNU2_TLS)
emit_insn (gen_tls_global_dynamic_64 (dest, x));
@@ -7673,7 +7676,7 @@ legitimize_tls_address (rtx x, enum tls_
if (TARGET_64BIT && ! TARGET_GNU2_TLS)
{
- rtx rax = gen_rtx_REG (Pmode, AX_REG), insns, note;
+ rtx rax = gen_rtx_REG (Pmode, AX_REG), insns, note, last;
start_sequence ();
emit_call_insn (gen_tls_local_dynamic_base_64 (rax));
@@ -7683,7 +7686,10 @@ legitimize_tls_address (rtx x, enum tls_
note = gen_rtx_EXPR_LIST (VOIDmode, const0_rtx, NULL);
note = gen_rtx_EXPR_LIST (VOIDmode, ix86_tls_get_addr (), note);
CONST_OR_PURE_CALL_P (insns) = 1;
- emit_libcall_block (insns, base, rax, note);
+/* emit_libcall_block (insns, base, rax, note); */
+ emit_insn (insns);
+ last = emit_move_insn (base, rax);
+ set_unique_reg_note (last, REG_EQUAL, note);
}
else if (TARGET_64BIT && TARGET_GNU2_TLS)
emit_insn (gen_tls_local_dynamic_base_64 (base));
--- gcc/dce.c.jj 2007-10-19 14:39:55.000000000 +0200
+++ gcc/dce.c 2007-10-19 18:01:08.000000000 +0200
@@ -102,7 +102,8 @@ deletable_insn_p (rtx insn, bool fast)
rtx body, x;
int i;
- if (!NONJUMP_INSN_P (insn))
+ if (!NONJUMP_INSN_P (insn)
+ && (!CALL_P (insn) || !CONST_OR_PURE_CALL_P (insn)))
return false;
body = PATTERN (insn);
Jakub