Re: [PATCH] [i386] Fix _mm256_zeroupper to notify LRA that vzeroupper will kill sse registers. [PR target/82735]

[Hongtao Liu <crazylht@gmail.com>]

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On Thu, May 27, 2021 at 6:50 PM Richard Sandiford
<richard.sandiford@arm.com> wrote:
>
> Jakub Jelinek <jakub@redhat.com> writes:
> > On Thu, May 27, 2021 at 01:07:09PM +0800, Hongtao Liu via Gcc-patches wrote:
> >> +  /* Flag used for call_insn indicates it's a fake call.  */
> >> +  RTX_FLAG (insn, used) = 1;
> >
> >> +      /* CALL_INSN use "used" flag to indicate it's a fake call.  */
> >> +      if (i == STACK_POINTER_REGNUM
> >> +      && !RTX_FLAG (insn_info->insn, used))
> >
> >> -      && ! SIBLING_CALL_P (insn))
> >> +      && ! SIBLING_CALL_P (insn)
> >> +      && !RTX_FLAG (insn, used))
> >
> >> -      /* For all other RTXes clear the used flag on the copy.  */
> >> -      RTX_FLAG (copy, used) = 0;
> >> +      /* For all other RTXes clear the used flag on the copy.
> >> +     CALL_INSN use "used" flag to indicate it's a fake call.  */
> >> +      if (!INSN_P (orig))
> >> +    RTX_FLAG (copy, used) = 0;
> >>        break;
> >>      }
> >>    return copy;
> >> @@ -57,7 +57,8 @@ requires_stack_frame_p (rtx_insn *insn, HARD_REG_SET prologue_used,
> >>    HARD_REG_SET hardregs;
> >>    unsigned regno;
> >>
> >> -  if (CALL_P (insn))
> >> +  /* CALL_INSN use "used" flag to indicate it's a fake call.  */
> >> +  if (CALL_P (insn) && !RTX_FLAG (insn, used))
> >>      return !SIBLING_CALL_P (insn);
> >
> > Please define a macro for this in rtl.h (and mention it above used;
> > member too in a comment, see all the other comments in there), like:
> > /* 1 if RTX is a call_insn for a fake call.  */
> > #define FAKE_CALL_P(RTX)                                      \
> >   (RTL_FLAG_CHECK1 ("FAKE_CALL_P", (RTX), CALL_INSN)->used)
Changed.
> > Though, I'm also not sure if used can be actually used for this,
> > because it is used e.g. in emit-rtl.c for verification of RTL sharing.
>
> I thought it should be OK, since:
>
> - copy_rtx_if_shared_1 and mark_used_flags do nothing for insns
> - verify_rtx_sharing is only called for parts of an insn, rather than
>   an insn itself
>
> I guess an alternative would be to add a new rtx_code for fake call
> insns and use CALL_P to test for both.  However, that would lose the
> property that the default behaviour is conservatively correct
> (even for direct checks of CALL_INSN), so the flag IMO seems better.
>
> Thanks,
> Richard
>
> > Though, it seems no other rtl flag is free for CALL_INSN.
> > Could this fake call flag sit on the CALL rtx instead?
> >
> >       Jakub

Updated separate patch for the middle-end part.

-- 
BR,
Hongtao

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From 537822e0d54aa324c520a4b504dcfe882b363c7b Mon Sep 17 00:00:00 2001
From: liuhongt <hongtao.liu@intel.com>
Date: Tue, 1 Jun 2021 09:00:57 +0800
Subject: [PATCH 1/2] CALL_INSN may not be a real function call.

Use "used" flag for CALL_INSN to indicate it's a fake call. If it's a
fake call, it won't have its own function stack.

gcc/ChangeLog

	PR target/82735
	* df-scan.c (df_get_call_refs): When call_insn is a fake call,
	it won't use stack pointer reg.
	* final.c (leaf_function_p): When call_insn is a fake call, it
	won't affect caller as a leaf function.
	* reg-stack.c (callee_clobbers_any_stack_reg): New.
	(subst_stack_regs): When call_insn doesn't clobber any stack
	reg, don't clear the arguments.
	* rtl.c (shallow_copy_rtx): Don't clear flag used when orig is
	a insn.
	* shrink-wrap.c (requires_stack_frame_p): No need for stack
	frame for a fake call.
	* rtl.h (FAKE_CALL_P): New macro.
---
 gcc/df-scan.c     |  3 ++-
 gcc/final.c       |  3 ++-
 gcc/reg-stack.c   | 18 +++++++++++++++++-
 gcc/rtl.c         |  6 ++++--
 gcc/rtl.h         |  5 +++++
 gcc/shrink-wrap.c |  2 +-
 6 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/gcc/df-scan.c b/gcc/df-scan.c
index 6691c3e8357..1268536b3f0 100644
--- a/gcc/df-scan.c
+++ b/gcc/df-scan.c
@@ -3090,7 +3090,8 @@ df_get_call_refs (class df_collection_rec *collection_rec,
 
   for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
     {
-      if (i == STACK_POINTER_REGNUM)
+      if (i == STACK_POINTER_REGNUM
+	  && !FAKE_CALL_P (insn_info->insn))
 	/* The stack ptr is used (honorarily) by a CALL insn.  */
 	df_ref_record (DF_REF_BASE, collection_rec, regno_reg_rtx[i],
 		       NULL, bb, insn_info, DF_REF_REG_USE,
diff --git a/gcc/final.c b/gcc/final.c
index e0a70fcd830..817f7722cb2 100644
--- a/gcc/final.c
+++ b/gcc/final.c
@@ -4109,7 +4109,8 @@ leaf_function_p (void)
   for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
     {
       if (CALL_P (insn)
-	  && ! SIBLING_CALL_P (insn))
+	  && ! SIBLING_CALL_P (insn)
+	  && ! FAKE_CALL_P (insn))
 	return 0;
       if (NONJUMP_INSN_P (insn)
 	  && GET_CODE (PATTERN (insn)) == SEQUENCE
diff --git a/gcc/reg-stack.c b/gcc/reg-stack.c
index 25210f0c17f..1d9ea035cf4 100644
--- a/gcc/reg-stack.c
+++ b/gcc/reg-stack.c
@@ -174,6 +174,7 @@
 #include "reload.h"
 #include "tree-pass.h"
 #include "rtl-iter.h"
+#include "function-abi.h"
 
 #ifdef STACK_REGS
 
@@ -2368,6 +2369,18 @@ subst_asm_stack_regs (rtx_insn *insn, stack_ptr regstack)
 	    }
       }
 }
+
+/* Return true if a function call is allowed to alter some or all bits
+   of any stack reg.  */
+static bool
+callee_clobbers_any_stack_reg (const function_abi & callee_abi)
+{
+  for (unsigned regno = FIRST_STACK_REG; regno <= LAST_STACK_REG; regno++)
+    if (callee_abi.clobbers_at_least_part_of_reg_p (regno))
+      return true;
+  return false;
+}
+
 \f
 /* Substitute stack hard reg numbers for stack virtual registers in
    INSN.  Non-stack register numbers are not changed.  REGSTACK is the
@@ -2382,7 +2395,10 @@ subst_stack_regs (rtx_insn *insn, stack_ptr regstack)
   bool control_flow_insn_deleted = false;
   int i;
 
-  if (CALL_P (insn))
+  /* If the target of the call doesn't clobber any stack registers,
+     Don't clear the arguments.  */
+  if (CALL_P (insn)
+      && callee_clobbers_any_stack_reg (insn_callee_abi (insn)))
     {
       int top = regstack->top;
 
diff --git a/gcc/rtl.c b/gcc/rtl.c
index b0ba1ff684c..aaee882f5ca 100644
--- a/gcc/rtl.c
+++ b/gcc/rtl.c
@@ -395,8 +395,10 @@ shallow_copy_rtx (const_rtx orig MEM_STAT_DECL)
     case SCRATCH:
       break;
     default:
-      /* For all other RTXes clear the used flag on the copy.  */
-      RTX_FLAG (copy, used) = 0;
+      /* For all other RTXes clear the used flag on the copy.
+	 CALL_INSN use "used" flag to indicate it's a fake call.  */
+      if (!INSN_P (orig))
+	RTX_FLAG (copy, used) = 0;
       break;
     }
   return copy;
diff --git a/gcc/rtl.h b/gcc/rtl.h
index 35178b5bfac..5ed0d6dd6fa 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -839,6 +839,11 @@ struct GTY(()) rtvec_def {
 /* Predicate yielding nonzero iff X is a call insn.  */
 #define CALL_P(X) (GET_CODE (X) == CALL_INSN)
 
+/* 1 if RTX is a call_insn for a fake call.
+   CALL_INSN use "used" flag to indicate it's a fake call.  */
+#define FAKE_CALL_P(RTX)                                        \
+  (RTL_FLAG_CHECK1 ("FAKE_CALL_P", (RTX), CALL_INSN)->used)
+
 /* Predicate yielding nonzero iff X is an insn that cannot jump.  */
 #define NONJUMP_INSN_P(X) (GET_CODE (X) == INSN)
 
diff --git a/gcc/shrink-wrap.c b/gcc/shrink-wrap.c
index ba7b5cd56fd..5e60f34f749 100644
--- a/gcc/shrink-wrap.c
+++ b/gcc/shrink-wrap.c
@@ -57,7 +57,7 @@ requires_stack_frame_p (rtx_insn *insn, HARD_REG_SET prologue_used,
   HARD_REG_SET hardregs;
   unsigned regno;
 
-  if (CALL_P (insn))
+  if (CALL_P (insn) && !FAKE_CALL_P (insn))
     return !SIBLING_CALL_P (insn);
 
   /* We need a frame to get the unique CFA expected by the unwinder.  */
-- 
2.18.1