Re: [PATCH, AARCH64] Enable fuse-caller-save for AARCH64

[Tom de Vries <Tom_deVries at mentor dot com>]

On 19-06-14 05:53, Richard Henderson wrote:
> On 06/01/2014 03:00 AM, Tom de Vries wrote:
> > >+aarch64_emit_call_insn (rtx pat)
> > >+{
> > >+  rtx insn = emit_call_insn (pat);
> > >+
> > >+  rtx *fusage = &CALL_INSN_FUNCTION_USAGE (insn);
> > >+  clobber_reg (fusage, gen_rtx_REG (word_mode, IP0_REGNUM));
> > >+  clobber_reg (fusage, gen_rtx_REG (word_mode, IP1_REGNUM));
> Actually, I'd like to know more about how this is supposed to work.
>
> Why are you only marking the two registers that would be used by a PLT entry,
> but not those clobbered by the ld.so trampoline, or indeed the unknown function
> that would be called from the PLT.
>
> Oh, I see, looking at the code we do actually follow the cgraph and make sure
> it is a direct call with a known destination.  So, in fact, it's only the
> registers that could be clobbered by ld branch islands (so these two are still
> correct for aarch64).
>
> This means the documentation is actually wrong when it mentions PLTs at all.

Yes, if we go from the point of view that the 
TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS hooks sole purpose is to enable 
the fuse-caller-save optimization.

How about this updated definition ? OK for trunk if re-testing on arm succeeds ?

Thanks,
- Tom


2014-06-19  Tom de Vries  <tom@codesourcery.com>

	* config/arm/arm.c (arm_emit_call_insn): Remove clobber of CC_REGNUM.
	* target.def: Update defition.
	* doc/tm.texi: Regenerate.

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index d293b5b..178f08b 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -17642,11 +17642,11 @@ arm_emit_call_insn (rtx pat, rtx addr, bool sibcall)
   if (TARGET_AAPCS_BASED)
     {
       /* For AAPCS, IP and CC can be clobbered by veneers inserted by the
-	 linker.  We need to add these to allow setting
-	 TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS to true.  */
+	 linker.  We need to add IP to allow setting
+	 TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS to true.  CC is not
+	 needed since it's a fixed register.  */
       rtx *fusage = &CALL_INSN_FUNCTION_USAGE (insn);
       clobber_reg (fusage, gen_rtx_REG (word_mode, IP_REGNUM));
-      clobber_reg (fusage, gen_rtx_REG (word_mode, CC_REGNUM));
     }
 }
 
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index c272630..b0a8dbd 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -4884,14 +4884,11 @@ Whether this target supports splitting the stack when the options described in @
 @cindex miscellaneous register hooks
 
 @deftypevr {Target Hook} bool TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS
-set to true if all the calls in the current function contain clobbers in
-CALL_INSN_FUNCTION_USAGE for the registers that are clobbered by the call
-rather than by the callee, and are not already set or clobbered in the call
-pattern.  Examples of such registers are registers used in PLTs and stubs,
-and temporary registers used in the call instruction but not present in the
-rtl pattern.  Another way to formulate it is the registers not present in the
-rtl pattern that are clobbered by the call assuming the callee does not
-clobber any register.  The default version of this hook is set to false.
+Set to true if each call that binds to a local definition contain clobbers
+in CALL_INSN_FUNCTION_USAGE for the non-fixed registers that are clobbered by
+the call rather than by the callee, and are not already set or clobbered in
+the call pattern.  The default version of this hook is set to false.  The
+purpose of this hook it to enable the fuse-caller-save optimization.
 @end deftypevr
 
 @node Varargs
diff --git a/gcc/target.def b/gcc/target.def
index e455211..b738281 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -5128,18 +5128,15 @@ FRAME_POINTER_REGNUM, ARG_POINTER_REGNUM, and the PIC_OFFSET_TABLE_REGNUM.",
  hook_void_bitmap)
 
 /* Targets should define this target hook to mark that non-callee clobbers are
-   present in CALL_INSN_FUNCTION_USAGE for all the calls in the current
-   function.  */
+   present in CALL_INSN_FUNCTION_USAGE for all the calls that bind to a local
+   definition.  */
 DEFHOOKPOD
 (call_fusage_contains_non_callee_clobbers,
- "set to true if all the calls in the current function contain clobbers in\n\
-CALL_INSN_FUNCTION_USAGE for the registers that are clobbered by the call\n\
-rather than by the callee, and are not already set or clobbered in the call\n\
-pattern.  Examples of such registers are registers used in PLTs and stubs,\n\
-and temporary registers used in the call instruction but not present in the\n\
-rtl pattern.  Another way to formulate it is the registers not present in the\n\
-rtl pattern that are clobbered by the call assuming the callee does not\n\
-clobber any register.  The default version of this hook is set to false.",
+ "Set to true if each call that binds to a local definition contain clobbers\n\
+in CALL_INSN_FUNCTION_USAGE for the non-fixed registers that are clobbered by\n\
+the call rather than by the callee, and are not already set or clobbered in\n\
+the call pattern.  The default version of this hook is set to false.  The\n\
+purpose of this hook it to enable the fuse-caller-save optimization.",
  bool, 
  false)
 
-- 
1.9.1