On Wed, 2023-11-15 at 04:42 +0800, Xi Ruoyao wrote:
> > There seems a better solution as suggested by the GCC internal doc.
> > Section 18.9.16 mentions -fipa-ra:
> >
> > -- Target Hook: bool TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS
> > Set to true if each call that binds to a local definition
> > explicitly clobbers or sets all non-fixed registers modified by
> > performing the call. That is, by the call pattern itself, or by
> > code that might be inserted by the linker (e.g. stubs, veneers,
> > branch islands), but not including those modifiable by the callee.
> > The affected registers may be mentioned explicitly in the call
> > pattern, or included as clobbers in CALL_INSN_FUNCTION_USAGE. The
> > default version of this hook is set to false. The purpose of this
> > hook is to enable the fipa-ra optimization.
> >
> > So we can add t0 into CALL_INSN_FUNCTION_USAGE of the call insn, like:
> >
> > diff --git a/gcc/config/loongarch/loongarch.md
> > b/gcc/config/loongarch/loongarch.md
> > index ea36542b1c3..96e7e98e6b3 100644
> > --- a/gcc/config/loongarch/loongarch.md
> > +++ b/gcc/config/loongarch/loongarch.md
> > @@ -3274,7 +3274,14 @@ (define_expand "sibcall"
> > XEXP (target, 1),
> > operands[1]));
> > else
> > - emit_call_insn (gen_sibcall_internal (target, operands[1]));
> > + {
> > + rtx call = gen_sibcall_internal (target, operands[1]);
> > +
> > + if (TARGET_CMODEL_MEDIUM && !REG_P (target))
> > + clobber_reg (&CALL_INSN_FUNCTION_USAGE (call),
> > + gen_rtx_REG (Pmode, T0_REGNUM));
> > + emit_call_insn (call);
> > + }
> > DONE;
> > })
> >
> > Likewise for sibcall_value.
>
> Nope. This does not work for
>
> __attribute__((noinline)) void q() { asm ("":::"memory"); }
> __attribute__((noinline)) static void t() { q(); }
>
> int
> main ()
> {
> int x0 = 114514;
>
> asm("":"+r"(x0));
> t();
> if (x0 != 114514)
> __builtin_trap ();
> }
>
> Not sure why...
Alright, it should be
diff --git a/gcc/config/loongarch/loongarch.md
b/gcc/config/loongarch/loongarch.md
index ea36542b1c3..75c595abad7 100644
--- a/gcc/config/loongarch/loongarch.md
+++ b/gcc/config/loongarch/loongarch.md
@@ -3274,7 +3274,13 @@ (define_expand "sibcall"
XEXP (target, 1),
operands[1]));
else
- emit_call_insn (gen_sibcall_internal (target, operands[1]));
+ {
+ rtx call = emit_call_insn (gen_sibcall_internal (target, operands[1]));
+
+ if (TARGET_CMODEL_MEDIUM && !REG_P (target))
+ clobber_reg (&CALL_INSN_FUNCTION_USAGE (call),
+ gen_rtx_REG (Pmode, T0_REGNUM));
+ }
DONE;
})
instead.
--
Xi Ruoyao <xry...@xry111.site>
School of Aerospace Science and Technology, Xidian University
