From: Xi Ruoyao <xry111@xry111.site>
Date: Sat, 22 Feb 2025 07:34:54 +0000 (+0800)
Subject: LoongArch: Avoid unnecessary zero-initialization using LSX for scalar popcount
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=d7434f3babc5a954fa68dd0c8ce6d4e917a017c1;p=thirdparty%2Fgcc.git

LoongArch: Avoid unnecessary zero-initialization using LSX for scalar popcount

Now for __builtin_popcountl we are getting things like

	vrepli.b	$vr0,0
	vinsgr2vr.d	$vr0,$r4,0
	vpcnt.d	$vr0,$vr0
	vpickve2gr.du	$r4,$vr0,0
	slli.w	$r4,$r4,0
	jr  $r1

The "vrepli.b" instruction is introduced by the init-regs pass (see
PR61810 and all the issues it references).  To work it around, we can
use post-reload instead of define_expand: the "f" constraint will make
the compiler automatically move the scalar between GPR and FPR, and
reload is much later than init-regs so init-regs won't get in our way.

Now the code looks like:

	movgr2fr.d	$f0,$r4
	vpcnt.d	$vr0,$vr0
	movfr2gr.d	$r4,$f0
	jr  $r1

gcc/ChangeLog:

	* config/loongarch/loongarch.md (cntmap): Change to uppercase.
	(popcount<GPR:mode>2): Modify to a post reload split.
---

diff --git a/gcc/config/loongarch/loongarch.md b/gcc/config/loongarch/loongarch.md
index 2f4817d885c..ba668880ba5 100644
--- a/gcc/config/loongarch/loongarch.md
+++ b/gcc/config/loongarch/loongarch.md
@@ -1773,21 +1773,23 @@
 
 ;; This attribute used for get connection of scalar mode and corresponding
 ;; vector mode.
-(define_mode_attr cntmap [(SI "v4si") (DI "v2di")])
+(define_mode_attr cntmap [(SI "V4SI") (DI "V2DI")])
 
-(define_expand "popcount<mode>2"
-  [(set (match_operand:GPR 0 "register_operand")
-	(popcount:GPR (match_operand:GPR 1 "register_operand")))]
+(define_insn_and_split "popcount<mode>2"
+  [(set (match_operand:GPR 0 "register_operand" "=f")
+	(popcount:GPR (match_operand:GPR 1 "register_operand" "f")))]
   "ISA_HAS_LSX"
+  "#"
+  ;; Do the split very lately to work around init-regs unneeded zero-
+  ;; initialization from init-regs.  See PR61810 and all the referenced
+  ;; issues.
+  "&& reload_completed"
+  [(set (match_operand:<cntmap> 0 "register_operand" "=f")
+	(popcount:<cntmap>
+	  (match_operand:<cntmap> 1 "register_operand" "f")))]
 {
-  rtx in = operands[1];
-  rtx out = operands[0];
-  rtx vreg = <MODE>mode == SImode ? gen_reg_rtx (V4SImode) :
-				    gen_reg_rtx (V2DImode);
-  emit_insn (gen_lsx_vinsgr2vr_<size> (vreg, in, vreg, GEN_INT (1)));
-  emit_insn (gen_popcount<cntmap>2 (vreg, vreg));
-  emit_insn (gen_lsx_vpickve2gr_<size> (out, vreg, GEN_INT (0)));
-  DONE;
+  operands[0] = gen_rtx_REG (<cntmap>mode, REGNO (operands[0]));
+  operands[1] = gen_rtx_REG (<cntmap>mode, REGNO (operands[1]));
 })
 
 ;;