Re: [PATCH v4] DSE: Use the constant store source if possible

["H.J. Lu" <hjl.tools@gmail.com>]

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On Wed, Jun 1, 2022 at 12:20 AM Richard Sandiford
<richard.sandiford@arm.com> wrote:
>
> "H.J. Lu" <hjl.tools@gmail.com> writes:
> > On Mon, May 30, 2022 at 09:35:43AM +0100, Richard Sandiford wrote:
> >> "H.J. Lu" <hjl.tools@gmail.com> writes:
> >> > ---
> >> > RTL DSE tracks redundant constant stores within a basic block.  When RTL
> >> > loop invariant motion hoists a constant initialization out of the loop
> >> > into a separate basic block, the constant store value becomes unknown
> >> > within the original basic block.  When recording store for RTL DSE, check
> >> > if the source register is set only once to a constant by a non-partial
> >> > unconditional load.  If yes, record the constant as the constant store
> >> > source.  It eliminates unrolled zero stores after memset 0 in a loop
> >> > where a vector register is used as the zero store source.
> >> >
> >> > Extract find_single_def_src from loop-iv.cc and move it to df-core.cc:
> >> >
> >> > 1. Rename to df_find_single_def_src.
> >> > 2. Change the argument to rtx and use rtx_equal_p.
> >> > 3. Return null for partial or conditional defs.
> >> >
> >> > gcc/
> >> >
> >> >    PR rtl-optimization/105638
> >> >    * df-core.cc (df_find_single_def_sr): Moved and renamed from
> >> >    find_single_def_src in loop-iv.cc.  Change the argument to rtx
> >> >    and use rtx_equal_p.  Return null for partial or conditional
> >> >    defs.
> >> >    * df.h (df_find_single_def_src): New prototype.
> >> >    * dse.cc (record_store): Use the constant source if the source
> >> >    register is set only once.
> >> >    * loop-iv.cc (find_single_def_src): Moved to df-core.cc.
> >> >    (replace_single_def_regs): Replace find_single_def_src with
> >> >    df_find_single_def_src.
> >> >
> >> > gcc/testsuite/
> >> >
> >> >    PR rtl-optimization/105638
> >> >    * g++.target/i386/pr105638.C: New test.
> >> > ---
> >> >  gcc/df-core.cc                           | 44 +++++++++++++++++++++++
> >> >  gcc/df.h                                 |  1 +
> >> >  gcc/dse.cc                               | 14 ++++++++
> >> >  gcc/loop-iv.cc                           | 45 +-----------------------
> >> >  gcc/testsuite/g++.target/i386/pr105638.C | 44 +++++++++++++++++++++++
> >> >  5 files changed, 104 insertions(+), 44 deletions(-)
> >> >  create mode 100644 gcc/testsuite/g++.target/i386/pr105638.C
> >> >
> >> > diff --git a/gcc/df-core.cc b/gcc/df-core.cc
> >> > index a901b84878f..f9b4de8eb7a 100644
> >> > --- a/gcc/df-core.cc
> >> > +++ b/gcc/df-core.cc
> >> > @@ -2009,6 +2009,50 @@ df_reg_used (rtx_insn *insn, rtx reg)
> >> >    return df_find_use (insn, reg) != NULL;
> >> >  }
> >> >
> >> > +/* If REG has a single definition, return its known value, otherwise return
> >> > +   null.  */
> >> > +
> >> > +rtx
> >> > +df_find_single_def_src (rtx reg)
> >> > +{
> >> > +  rtx src = NULL_RTX;
> >> > +
> >> > +  /* Don't look through unbounded number of single definition REG copies,
> >> > +     there might be loops for sources with uninitialized variables.  */
> >> > +  for (int cnt = 0; cnt < 128; cnt++)
> >> > +    {
> >> > +      df_ref adef = DF_REG_DEF_CHAIN (REGNO (reg));
> >> > +      if (adef == NULL || DF_REF_NEXT_REG (adef) != NULL
> >> > +    || DF_REF_IS_ARTIFICIAL (adef)
> >> > +    || (DF_REF_FLAGS (adef)
> >> > +        & (DF_REF_PARTIAL | DF_REF_CONDITIONAL)))
> >> > +  return NULL_RTX;
> >> > +
> >> > +      rtx set = single_set (DF_REF_INSN (adef));
> >> > +      if (set == NULL || !rtx_equal_p (SET_DEST (set), reg))
> >> > +  return NULL_RTX;
> >> > +
> >> > +      rtx note = find_reg_equal_equiv_note (DF_REF_INSN (adef));
> >> > +      if (note && function_invariant_p (XEXP (note, 0)))
> >> > +  {
> >> > +    src = XEXP (note, 0);
> >> > +    break;
> >> > +  }
> >>
> >> Seems simpler to return this directly, rather than break and then
> >> check function_invariant_p again.
> >
> > Fixed.
> >
> >>
> >> > +      src = SET_SRC (set);
> >> > +
> >> > +      if (REG_P (src))
> >> > +  {
> >> > +    reg = src;
> >> > +    continue;
> >> > +  }
> >> > +      break;
> >> > +    }
> >> > +  if (!function_invariant_p (src))
> >> > +    return NULL_RTX;
> >> > +
> >> > +  return src;
> >> > +}
> >> > +
> >> >
> >> >  /*----------------------------------------------------------------------------
> >> >     Debugging and printing functions.
> >> > diff --git a/gcc/df.h b/gcc/df.h
> >> > index bd329205d08..71e249ad20a 100644
> >> > --- a/gcc/df.h
> >> > +++ b/gcc/df.h
> >> > @@ -991,6 +991,7 @@ extern df_ref df_find_def (rtx_insn *, rtx);
> >> >  extern bool df_reg_defined (rtx_insn *, rtx);
> >> >  extern df_ref df_find_use (rtx_insn *, rtx);
> >> >  extern bool df_reg_used (rtx_insn *, rtx);
> >> > +extern rtx df_find_single_def_src (rtx);
> >> >  extern void df_worklist_dataflow (struct dataflow *,bitmap, int *, int);
> >> >  extern void df_print_regset (FILE *file, const_bitmap r);
> >> >  extern void df_print_word_regset (FILE *file, const_bitmap r);
> >> > diff --git a/gcc/dse.cc b/gcc/dse.cc
> >> > index 30c11cee034..c915266f025 100644
> >> > --- a/gcc/dse.cc
> >> > +++ b/gcc/dse.cc
> >> > @@ -1508,6 +1508,20 @@ record_store (rtx body, bb_info_t bb_info)
> >> >
> >> >      if (tem && CONSTANT_P (tem))
> >> >        const_rhs = tem;
> >> > +    else
> >> > +      {
> >> > +        /* If RHS is set only once to a constant, set CONST_RHS
> >> > +           to the constant.  */
> >> > +        rtx def_src = df_find_single_def_src (rhs);
> >> > +        if (def_src != nullptr && CONSTANT_P (def_src))
> >> > +          {
> >> > +            df_ref def = DF_REG_DEF_CHAIN (REGNO (rhs));
> >> > +            rtx_insn *def_insn = DF_REF_INSN (def);
> >> > +            rtx def_body = single_set (def_insn);
> >> > +            if (rhs == SET_DEST (def_body))
> >> > +              const_rhs = def_src;
> >> > +          }
> >> > +      }
> >>
> >> This shouldn't be necessary now: we can rely on def_src being correct.
> >>
> >> I.e. I think this can just be:
> >>
> >>            rtx def_src = df_find_single_def_src (rhs);
> >>            if (def_src != nullptr && CONSTANT_P (def_src))
> >>              const_rhs = def_src;
> >
> > Fixed.
> >
> >>
> >> Thanks,
> >> Richard
> >>
> >
> > Here is the v4 patch.  OK for master?
> >
> > Thanks.
> >
> >
> > H.J.
> > ---
> > RTL DSE tracks redundant constant stores within a basic block.  When RTL
> > loop invariant motion hoists a constant initialization out of the loop
> > into a separate basic block, the constant store value becomes unknown
> > within the original basic block.  When recording store for RTL DSE, check
> > if the source register is set only once to a constant by a non-partial
> > unconditional load.  If yes, record the constant as the constant store
> > source.  It eliminates unrolled zero stores after memset 0 in a loop
> > where a vector register is used as the zero store source.
> >
> > gcc/
> >
> >       PR rtl-optimization/105638
> >       * df-core.cc (df_find_single_def_src): Moved and renamed from
> >       find_single_def_src in loop-iv.cc.  Change the argument to rtx
> >       and use rtx_equal_p.  Return null for partial or conditional
> >       defs.
> >       * df.h (df_find_single_def_src): New prototype.
> >       * dse.cc (record_store): Use the constant source if the source
> >       register is set only once.
> >       * loop-iv.cc (find_single_def_src): Moved to df-core.cc.
> >       (replace_single_def_regs): Replace find_single_def_src with
> >       df_find_single_def_src.
> >
> > gcc/testsuite/
> >
> >       PR rtl-optimization/105638
> >       * g++.target/i386/pr105638.C: New test.
> > ---
> >  gcc/df-core.cc                           | 44 +++++++++++++++++++++++
> >  gcc/df.h                                 |  1 +
> >  gcc/dse.cc                               |  8 +++++
> >  gcc/loop-iv.cc                           | 45 +-----------------------
> >  gcc/testsuite/g++.target/i386/pr105638.C | 44 +++++++++++++++++++++++
> >  5 files changed, 98 insertions(+), 44 deletions(-)
> >  create mode 100644 gcc/testsuite/g++.target/i386/pr105638.C
> >
> > diff --git a/gcc/df-core.cc b/gcc/df-core.cc
> > index a901b84878f..e56d9bcf760 100644
> > --- a/gcc/df-core.cc
> > +++ b/gcc/df-core.cc
> > @@ -2009,6 +2009,50 @@ df_reg_used (rtx_insn *insn, rtx reg)
> >    return df_find_use (insn, reg) != NULL;
> >  }
> >
> > +/* If REG has a single definition, return its known value, otherwise return
> > +   null.  */
> > +
> > +rtx
> > +df_find_single_def_src (rtx reg)
> > +{
> > +  rtx src = NULL_RTX;
> > +
> > +  /* Don't look through unbounded number of single definition REG copies,
> > +     there might be loops for sources with uninitialized variables.  */
> > +  for (int cnt = 0; cnt < 128; cnt++)
> > +    {
> > +      df_ref adef = DF_REG_DEF_CHAIN (REGNO (reg));
> > +      if (adef == NULL || DF_REF_NEXT_REG (adef) != NULL
> > +       || DF_REF_IS_ARTIFICIAL (adef)
> > +       || (DF_REF_FLAGS (adef)
> > +           & (DF_REF_PARTIAL | DF_REF_CONDITIONAL)))
> > +     return NULL_RTX;
> > +
> > +      rtx set = single_set (DF_REF_INSN (adef));
> > +      if (set == NULL || !rtx_equal_p (SET_DEST (set), reg))
> > +     return NULL_RTX;
> > +
> > +      rtx note = find_reg_equal_equiv_note (DF_REF_INSN (adef));
> > +      if (note && function_invariant_p (XEXP (note, 0)))
> > +     {
> > +       src = XEXP (note, 0);
> > +       return src;
>
> Seems simpler without the assignment:
>
>     return XEXP (note, 0);
>
> OK with that change, thanks.

Fixed.

> Richard
>
>

This is the patch I am checking in.

Thanks.

-- 
H.J.

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From 99d1fe3790275e0eaa588637f90f0ff1e5b8d117 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Wed, 18 May 2022 13:00:47 -0700
Subject: [PATCH] DSE: Use the constant store source if possible

RTL DSE tracks redundant constant stores within a basic block.  When RTL
loop invariant motion hoists a constant initialization out of the loop
into a separate basic block, the constant store value becomes unknown
within the original basic block.  When recording store for RTL DSE, check
if the source register is set only once to a constant by a non-partial
unconditional load.  If yes, record the constant as the constant store
source.  It eliminates unrolled zero stores after memset 0 in a loop
where a vector register is used as the zero store source.

gcc/

	PR rtl-optimization/105638
	* df-core.cc (df_find_single_def_src): Moved and renamed from
	find_single_def_src in loop-iv.cc.  Change the argument to rtx
	and use rtx_equal_p.  Return null for partial or conditional
	defs.
	* df.h (df_find_single_def_src): New prototype.
	* dse.cc (record_store): Use the constant source if the source
	register is set only once.
	* loop-iv.cc (find_single_def_src): Moved to df-core.cc.
	(replace_single_def_regs): Replace find_single_def_src with
	df_find_single_def_src.

gcc/testsuite/

	PR rtl-optimization/105638
	* g++.target/i386/pr105638.C: New test.
---
 gcc/df-core.cc                           | 41 +++++++++++++++++++++
 gcc/df.h                                 |  1 +
 gcc/dse.cc                               |  8 +++++
 gcc/loop-iv.cc                           | 45 +-----------------------
 gcc/testsuite/g++.target/i386/pr105638.C | 44 +++++++++++++++++++++++
 5 files changed, 95 insertions(+), 44 deletions(-)
 create mode 100644 gcc/testsuite/g++.target/i386/pr105638.C

diff --git a/gcc/df-core.cc b/gcc/df-core.cc
index a901b84878f..e3a56bf6a9f 100644
--- a/gcc/df-core.cc
+++ b/gcc/df-core.cc
@@ -2009,6 +2009,47 @@ df_reg_used (rtx_insn *insn, rtx reg)
   return df_find_use (insn, reg) != NULL;
 }
 
+/* If REG has a single definition, return its known value, otherwise return
+   null.  */
+
+rtx
+df_find_single_def_src (rtx reg)
+{
+  rtx src = NULL_RTX;
+
+  /* Don't look through unbounded number of single definition REG copies,
+     there might be loops for sources with uninitialized variables.  */
+  for (int cnt = 0; cnt < 128; cnt++)
+    {
+      df_ref adef = DF_REG_DEF_CHAIN (REGNO (reg));
+      if (adef == NULL || DF_REF_NEXT_REG (adef) != NULL
+	  || DF_REF_IS_ARTIFICIAL (adef)
+	  || (DF_REF_FLAGS (adef)
+	      & (DF_REF_PARTIAL | DF_REF_CONDITIONAL)))
+	return NULL_RTX;
+
+      rtx set = single_set (DF_REF_INSN (adef));
+      if (set == NULL || !rtx_equal_p (SET_DEST (set), reg))
+	return NULL_RTX;
+
+      rtx note = find_reg_equal_equiv_note (DF_REF_INSN (adef));
+      if (note && function_invariant_p (XEXP (note, 0)))
+	return XEXP (note, 0);
+      src = SET_SRC (set);
+
+      if (REG_P (src))
+	{
+	  reg = src;
+	  continue;
+	}
+      break;
+    }
+  if (!function_invariant_p (src))
+    return NULL_RTX;
+
+  return src;
+}
+
 \f
 /*----------------------------------------------------------------------------
    Debugging and printing functions.
diff --git a/gcc/df.h b/gcc/df.h
index bd329205d08..71e249ad20a 100644
--- a/gcc/df.h
+++ b/gcc/df.h
@@ -991,6 +991,7 @@ extern df_ref df_find_def (rtx_insn *, rtx);
 extern bool df_reg_defined (rtx_insn *, rtx);
 extern df_ref df_find_use (rtx_insn *, rtx);
 extern bool df_reg_used (rtx_insn *, rtx);
+extern rtx df_find_single_def_src (rtx);
 extern void df_worklist_dataflow (struct dataflow *,bitmap, int *, int);
 extern void df_print_regset (FILE *file, const_bitmap r);
 extern void df_print_word_regset (FILE *file, const_bitmap r);
diff --git a/gcc/dse.cc b/gcc/dse.cc
index 30c11cee034..994c60dc189 100644
--- a/gcc/dse.cc
+++ b/gcc/dse.cc
@@ -1508,6 +1508,14 @@ record_store (rtx body, bb_info_t bb_info)
 
 	  if (tem && CONSTANT_P (tem))
 	    const_rhs = tem;
+	  else
+	    {
+	      /* If RHS is set only once to a constant, set CONST_RHS
+		 to the constant.  */
+	      rtx def_src = df_find_single_def_src (rhs);
+	      if (def_src != nullptr && CONSTANT_P (def_src))
+		const_rhs = def_src;
+	    }
 	}
     }
 
diff --git a/gcc/loop-iv.cc b/gcc/loop-iv.cc
index 0eafe7d2362..d639336445a 100644
--- a/gcc/loop-iv.cc
+++ b/gcc/loop-iv.cc
@@ -1378,49 +1378,6 @@ simple_rhs_p (rtx rhs)
     }
 }
 
-/* If REGNO has a single definition, return its known value, otherwise return
-   null.  */
-
-static rtx
-find_single_def_src (unsigned int regno)
-{
-  rtx src = NULL_RTX;
-
-  /* Don't look through unbounded number of single definition REG copies,
-     there might be loops for sources with uninitialized variables.  */
-  for (int cnt = 0; cnt < 128; cnt++)
-    {
-      df_ref adef = DF_REG_DEF_CHAIN (regno);
-      if (adef == NULL || DF_REF_NEXT_REG (adef) != NULL
-	  || DF_REF_IS_ARTIFICIAL (adef))
-	return NULL_RTX;
-
-      rtx set = single_set (DF_REF_INSN (adef));
-      if (set == NULL || !REG_P (SET_DEST (set))
-	  || REGNO (SET_DEST (set)) != regno)
-	return NULL_RTX;
-
-      rtx note = find_reg_equal_equiv_note (DF_REF_INSN (adef));
-      if (note && function_invariant_p (XEXP (note, 0)))
-	{
-	  src = XEXP (note, 0);
-	  break;
-	}
-      src = SET_SRC (set);
-
-      if (REG_P (src))
-	{
-	  regno = REGNO (src);
-	  continue;
-	}
-      break;
-    }
-  if (!function_invariant_p (src))
-    return NULL_RTX;
-
-  return src;
-}
-
 /* If any registers in *EXPR that have a single definition, try to replace
    them with the known-equivalent values.  */
 
@@ -1433,7 +1390,7 @@ replace_single_def_regs (rtx *expr)
     {
       rtx x = *iter;
       if (REG_P (x))
-	if (rtx new_x = find_single_def_src (REGNO (x)))
+	if (rtx new_x = df_find_single_def_src (x))
 	  {
 	    *expr = simplify_replace_rtx (*expr, x, new_x);
 	    goto repeat;
diff --git a/gcc/testsuite/g++.target/i386/pr105638.C b/gcc/testsuite/g++.target/i386/pr105638.C
new file mode 100644
index 00000000000..ff40a459de1
--- /dev/null
+++ b/gcc/testsuite/g++.target/i386/pr105638.C
@@ -0,0 +1,44 @@
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-options "-std=gnu++20 -O2 -march=skylake" } */
+/* { dg-final { scan-assembler-not "vpxor" } } */
+
+#include <stdint.h>
+#include <vector>
+#include <tr1/array>
+
+class FastBoard {
+public:
+    typedef std::pair<int, int> movescore_t;
+    typedef std::tr1::array<movescore_t, 24> scoredlist_t;
+    
+protected:
+    std::vector<int> m_critical;
+
+    int m_boardsize;    
+};
+
+class FastState {
+public:        
+    FastBoard board;
+    
+    int movenum;              
+protected:
+    FastBoard::scoredlist_t scoredmoves;
+};
+
+class KoState : public FastState {
+private:         
+    std::vector<uint64_t> ko_hash_history;   
+    std::vector<uint64_t> hash_history;     
+};
+
+class GameState : public KoState {
+public:                    
+    void foo ();      
+private:
+    std::vector<KoState> game_history;                          
+};
+
+void GameState::foo() {
+    game_history.resize(movenum);
+}
-- 
2.36.1