[PATCH, RFC] combine: Don't truncate const operand of AND if it's no benefits

[HAO CHEN GUI <guihaoc@linux.ibm.com>]

Hi,
  This patch tries to fix the problem when a canonical form doesn't benefit
on a specific target. The const operand of AND is and with the nonzero
bits of another operand in combine pass. It's a canonical form, but it's no
benefits for the target which has rotate and mask insns. As the mask is
truncated, it can't match the insn conditions which it originally matches.
For example, the following insn condition checks the sum of two AND masks.
When one of the mask is truncated, the condition breaks.

(define_insn "*rotlsi3_insert_5"
  [(set (match_operand:SI 0 "gpc_reg_operand" "=r,r")
	(ior:SI (and:SI (match_operand:SI 1 "gpc_reg_operand" "0,r")
			(match_operand:SI 2 "const_int_operand" "n,n"))
		(and:SI (match_operand:SI 3 "gpc_reg_operand" "r,0")
			(match_operand:SI 4 "const_int_operand" "n,n"))))]
  "rs6000_is_valid_mask (operands[2], NULL, NULL, SImode)
   && UINTVAL (operands[2]) != 0 && UINTVAL (operands[4]) != 0
   && UINTVAL (operands[2]) + UINTVAL (operands[4]) + 1 == 0"
...

  This patch tries to fix the problem by comparing the rtx cost. If another
operand (varop) is not changed and rtx cost with new mask is not less than
the original one, the mask is restored to original one.

  I'm not sure if comparison of rtx cost here is proper. The outer code is
unknown and I suppose it as "SET". Also the rtx cost might not be accurate.
From my understanding, the canonical forms should always benefit as it can't
be undo in combine pass. Do we have a perfect solution for this kind of
issues? Looking forward for your advice.

  Another similar issues for canonical forms. Whether the widen mode for
lshiftrt is always good?
https://gcc.gnu.org/pipermail/gcc-patches/2023-July/624852.html

Thanks
Gui Haochen

ChangeLog
Combine: Don't truncate const operand of AND if it's no benefits

In combine pass, the canonical form is to turn off all bits in the constant
that are know to already be zero for AND.

  /* Turn off all bits in the constant that are known to already be zero.
     Thus, if the AND isn't needed at all, we will have CONSTOP == NONZERO_BITS
     which is tested below.  */

  constop &= nonzero;

But it doesn't benefit when the target has rotate and mask insert insns.
The AND mask is truncated and lost its information.  Thus it can't match
the insn conditions.  For example, the following insn condition checks
the sum of two AND masks.

(define_insn "*rotlsi3_insert_5"
  [(set (match_operand:SI 0 "gpc_reg_operand" "=r,r")
	(ior:SI (and:SI (match_operand:SI 1 "gpc_reg_operand" "0,r")
			(match_operand:SI 2 "const_int_operand" "n,n"))
		(and:SI (match_operand:SI 3 "gpc_reg_operand" "r,0")
			(match_operand:SI 4 "const_int_operand" "n,n"))))]
  "rs6000_is_valid_mask (operands[2], NULL, NULL, SImode)
   && UINTVAL (operands[2]) != 0 && UINTVAL (operands[4]) != 0
   && UINTVAL (operands[2]) + UINTVAL (operands[4]) + 1 == 0"
...

This patch restores the const operand of AND if the another operand is
not optimized and the truncated const operand doesn't save the rtx cost.

gcc/
	* combine.cc (simplify_and_const_int_1): Restore the const operand
	of AND if varop is not optimized and the rtx cost of the new const
	operand is not reduced.

gcc/testsuite/
	* gcc.target/powerpc/rlwimi-0.c: Reduced total number of insns and
	adjust the number of rotate and mask insns.
	* gcc.target/powerpc/rlwimi-1.c: Likewise.
	* gcc.target/powerpc/rlwimi-2.c: Likewise.

patch.diff
diff --git a/gcc/combine.cc b/gcc/combine.cc
index a4479f8d836..16ff09ea854 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -10161,8 +10161,23 @@ simplify_and_const_int_1 (scalar_int_mode mode, rtx varop,
   if (constop == nonzero)
     return varop;

-  if (varop == orig_varop && constop == orig_constop)
-    return NULL_RTX;
+  if (varop == orig_varop)
+    {
+      if (constop == orig_constop)
+	return NULL_RTX;
+      else
+	{
+	  rtx tmp = simplify_gen_binary (AND, mode, varop,
+					 gen_int_mode (constop, mode));
+	  rtx orig = simplify_gen_binary (AND, mode, varop,
+					  gen_int_mode (orig_constop, mode));
+	  if (set_src_cost (tmp, mode, optimize_this_for_speed_p)
+	      < set_src_cost (orig, mode, optimize_this_for_speed_p))
+	    return tmp;
+	  else
+	    return NULL_RTX;
+	}
+    }

   /* Otherwise, return an AND.  */
   return simplify_gen_binary (AND, mode, varop, gen_int_mode (constop, mode));
diff --git a/gcc/testsuite/gcc.target/powerpc/rlwimi-0.c b/gcc/testsuite/gcc.target/powerpc/rlwimi-0.c
index 961be199901..d9dd4419f1d 100644
--- a/gcc/testsuite/gcc.target/powerpc/rlwimi-0.c
+++ b/gcc/testsuite/gcc.target/powerpc/rlwimi-0.c
@@ -2,15 +2,15 @@
 /* { dg-options "-O2" } */

 /* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 16485 { target ilp32 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 19909 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 19780 { target lp64 } } } */
 /* { dg-final { scan-assembler-times {(?n)^\s+blr} 6750 } } */
 /* { dg-final { scan-assembler-times {(?n)^\s+mr} 3007 { target ilp32 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+mr} 11 { target lp64 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+rldicl} 6420 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+mr} 140 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+rldicl} 6162 { target lp64 } } } */

 /* { dg-final { scan-assembler-times {(?n)^\s+rlwimi} 6420 { target ilp32 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+rldimi} 310 { target lp64 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+rlwimi} 6110 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+rldimi} 366 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+rlwimi} 6054 { target lp64 } } } */
 /* { dg-final { scan-assembler-times {(?n)^\s+rotlwi} 308 } } */


diff --git a/gcc/testsuite/gcc.target/powerpc/rlwimi-1.c b/gcc/testsuite/gcc.target/powerpc/rlwimi-1.c
index e2c607b1d45..d955fc792d9 100644
--- a/gcc/testsuite/gcc.target/powerpc/rlwimi-1.c
+++ b/gcc/testsuite/gcc.target/powerpc/rlwimi-1.c
@@ -2,15 +2,15 @@
 /* { dg-options "-O2" } */

 /* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 13977 { target ilp32 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 20217 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 20189 { target lp64 } } } */
 /* { dg-final { scan-assembler-times {(?n)^\s+blr} 6750 } } */
 /* { dg-final { scan-assembler-times {(?n)^\s+mr} 499 { target ilp32 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+mr} 11 { target lp64 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+rldicl} 6728 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+mr} 39 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+rldicl} 6672 { target lp64 } } } */

 /* { dg-final { scan-assembler-times {(?n)^\s+rlwimi} 1404 { target ilp32 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+rldimi} 134 { target lp64 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+rlwimi} 1270 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+rldimi} 190 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+rlwimi} 1214 { target lp64 } } } */

 /* { dg-final { scan-assembler-times {(?n)^\s+mulli} 5324 } } */

diff --git a/gcc/testsuite/gcc.target/powerpc/rlwimi-2.c b/gcc/testsuite/gcc.target/powerpc/rlwimi-2.c
index bafa371db73..9abfd7abf08 100644
--- a/gcc/testsuite/gcc.target/powerpc/rlwimi-2.c
+++ b/gcc/testsuite/gcc.target/powerpc/rlwimi-2.c
@@ -2,14 +2,14 @@
 /* { dg-options "-O2" } */

 /* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 14121 { target ilp32 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 20217 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 19622 { target lp64 } } } */
 /* { dg-final { scan-assembler-times {(?n)^\s+blr} 6750 } } */
 /* { dg-final { scan-assembler-times {(?n)^\s+mr} 643 { target ilp32 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+mr} 11 { target lp64 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+rldicl} 7790 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+mr} 658 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+rldicl} 5460 { target lp64 } } } */

 /* { dg-final { scan-assembler-times {(?n)^\s+rlwimi} 1692 { target ilp32 } } } */
-/* { dg-final { scan-assembler-times {(?n)^\s+rlwimi} 1666 { target lp64 } } } */
+/* { dg-final { scan-assembler-times {(?n)^\s+rlwimi} 1610 { target lp64 } } } */

 /* { dg-final { scan-assembler-times {(?n)^\s+mulli} 5036 } } */