Re: [PATCH] rs6000: Define movsf_from_si2 to extract high part SF element from DImode[PR89310]

[luoxhu <luoxhu@linux.ibm.com>]

Hi,

On 2020/7/10 03:25, Segher Boessenkool wrote:
> Hi!
> 
> On Thu, Jul 09, 2020 at 11:09:42AM +0800, luoxhu wrote:
>>> Maybe change it back to just SI?  It won't match often at all for QI or
>>> HI anyway, it seems.  Sorry for that detour.  Should be good with the
>>> above nits fixed :-)
>>
>> OK, if I see correctly, subreg of DImode should be SImode and I used
>> subreg:SI to match only SI, so no need to consider mask for QI and HI? :)
> 
> My problem with it was that the shift amounts won't be 32 for QI etc.?

But if the subreg:SI only accepts SImode comes in, why do we need handle the
shift amounts for QI/HI? It not using QHSI here...

> 
>> +;;     {%1:SF=unspec[r122:DI>>0x20#0] 86;clobber scratch;}
>> +;; split it before reload with "and mask" to avoid generating shift right
>> +;; 32 bit then shift left 32 bit.
>> +(define_insn_and_split "movsf_from_si2"
>> +  [(set (match_operand:SF 0 "gpc_reg_operand" "=wa")
>> +	    (unspec:SF [
>> +	     (subreg:SI (
>> +		 ashiftrt:DI (
> 
> Opening parens *start* a line, they never end it.  So:
> 
> (define_insn_and_split "movsf_from_si2"
>    [(set (match_operand:SF 0 "vsx_reg_sfsubreg_ok" "=wa")
> 	  (unspec:SF
> 	    [(subreg:SI
> 	       (ashiftrt:DI
> 		 (match_operand:DI 1 "input_operand" "r")
> 		 (const_int 32))
> 	      0)]
> 	    UNSPEC_SF_FROM_SI))
>     (clobber (match_scratch:DI 2 "=r"))]
> 
> or something like that.  There aren't really any real rules...  The
> important points are that nested things should be indented, and things
> at the same level should have the same indent (like the outer set and
> clobber).  The [ for an unspec is sometimes put at the end of a line,
> that reads a little better perhaps.

OK, seems the md file needs a format tool too...

> 
>> +  "TARGET_NO_SF_SUBREG"
>> +  "#"
>> +  "&& vsx_reg_sfsubreg_ok (operands[0], SFmode)"
> 
> Put this in the insn condition?  And since this is just a predicate,
> you can just use it instead of gpc_reg_operand.
> 
> (The split condition becomes "&& 1" then, not "").

OK, this seems a bit strange as movsi_from_sf, movsf_from_si and
movdi_from_sf_zero_ext all use it as condition...

And why vsx_reg_sfsubreg_ok allows "SF SUBREGS" and TARGET_NO_SF_SUBREG
"avoid (SUBREG:SF (REG:SI)", I guess they are not the same meaning? (The 
TARGET_NO_SF_SUBREG is also copied from other similar defines.)  Thanks.


Updated patch and correct the title:


Define movsf_from_si2 to extract high part SF element from DImode[PR89310]


For extracting high part element from DImode register like:

{%1:SF=unspec[r122:DI>>0x20#0] 86;clobber scratch;}

split it before reload with "and mask" to avoid generating shift right
32 bit then shift left 32 bit.  This pattern also exists in PR42475 and
PR67741, etc.

srdi 3,3,32
sldi 9,3,32
mtvsrd 1,9
xscvspdpn 1,1

=>

rldicr 3,3,0,31
mtvsrd 1,3
xscvspdpn 1,1

Bootstrap and regression tested pass on Power8-LE.

gcc/ChangeLog:

2020-07-08  Xionghu Luo  <luoxhu@linux.ibm.com>

	PR rtl-optimization/89310
	* config/rs6000/rs6000.md (movsf_from_si2): New
	define_insn_and_split.

gcc/testsuite/ChangeLog:

2020-07-08  Xionghu Luo  <luoxhu@linux.ibm.com>

	PR rtl-optimization/89310
	* gcc.target/powerpc/pr89310.c: New test.
---
 gcc/config/rs6000/rs6000.md                | 32 ++++++++++++++++++++++
 gcc/testsuite/gcc.target/powerpc/pr89310.c | 17 ++++++++++++
 2 files changed, 49 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/powerpc/pr89310.c

diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md
index 4fcd6a94022..2331c84dcbd 100644
--- a/gcc/config/rs6000/rs6000.md
+++ b/gcc/config/rs6000/rs6000.md
@@ -7593,6 +7593,38 @@ (define_insn_and_split "movsf_from_si"
 	    "*,          *,         p9v,       p8v,       *,         *,
 	     p8v,        p8v,       p8v,       *")])
 
+;; For extracting high part element from DImode register like:
+;;     {%1:SF=unspec[r122:DI>>0x20#0] 86;clobber scratch;}
+;; split it before reload with "and mask" to avoid generating shift right
+;; 32 bit then shift left 32 bit.
+(define_insn_and_split "movsf_from_si2"
+  [(set (match_operand:SF 0 "vsx_reg_sfsubreg_ok" "=wa")
+	    (unspec:SF
+	     [(subreg:SI
+	       (ashiftrt:DI
+		(match_operand:DI 1 "input_operand" "r")
+		(const_int 32))
+	       0)]
+	     UNSPEC_SF_FROM_SI))
+  (clobber (match_scratch:DI 2 "=r"))]
+  "TARGET_NO_SF_SUBREG"
+  "#"
+  "&& 1"
+  [(const_int 0)]
+{
+  if (GET_CODE (operands[2]) == SCRATCH)
+    operands[2] = gen_reg_rtx (DImode);
+
+  rtx mask = GEN_INT (HOST_WIDE_INT_M1U << 32);
+  emit_insn (gen_anddi3 (operands[2], operands[1], mask));
+  emit_insn (gen_p8_mtvsrd_sf (operands[0], operands[2]));
+  emit_insn (gen_vsx_xscvspdpn_directmove (operands[0], operands[0]));
+  DONE;
+}
+  [(set_attr "length" "12")
+  (set_attr "type" "vecfloat")
+  (set_attr "isa" "p8v")])
 
 ;; Move 64-bit binary/decimal floating point
 (define_expand "mov<mode>"
diff --git a/gcc/testsuite/gcc.target/powerpc/pr89310.c b/gcc/testsuite/gcc.target/powerpc/pr89310.c
new file mode 100644
index 00000000000..15e78509246
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr89310.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+struct s {
+  int i;
+  float f;
+};
+
+float
+foo (struct s arg)
+{
+  return arg.f;
+}
+
+/* { dg-final { scan-assembler-not {\msrdi\M} } } */
+/* { dg-final { scan-assembler-not {\msldi\M} } } */
+/* { dg-final { scan-assembler-times {\mrldicr\M} 1 } } */
-- 
2.21.0.777.g83232e3864