[Bug target/17381] Unnecessary register move for float extend

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=17381

--- Comment #9 from Martin Sebor  ---
Author: msebor
Date: Thu Jan 28 21:05:39 2016
New Revision: 232947

URL: https://gcc.gnu.org/viewcvs?rev=232947=gcc=rev
Log:
PR target/17381 - Unnecessary register move for float extend

2016-01-28  Martin Sebor  

PR target/17381
* gcc.target/powerpc/pr17381.c: New test.

Added:
trunk/gcc/testsuite/gcc.target/powerpc/pr17381.c
Modified:
trunk/gcc/testsuite/ChangeLog

[Bug target/17381] Unnecessary register move for float extend

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=17381

Martin Sebor  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 CC||msebor at gcc dot gnu.org
 Resolution|--- |FIXED

--- Comment #8 from Martin Sebor  ---
Trunk as well as the native 4.8.3 on RHEL 7.1 do not emit the redundant fmr
instruction.  Below is what I get today.  Closing as fixed.

$ /build/gcc-trunk/gcc/xgcc -B /build/gcc-trunk/gcc -O2 -S -Wall -Wextra
-Wpedantic -m32 -o/dev/stdout ~/tmp/t.c
.file   "t.c"
.machine power4
.section".text"
.align 2
.p2align 4,,15
.globl test1
.type   test1, @function
test1:
fmr 0,1
lis 9,f@ha
stfs 1,f@l(9)
lis 9,d@ha
stfd 0,d@l(9)
blr
.size   test1,.-test1
.comm   f,4,4
.comm   d,8,8
.ident  "GCC: (GNU) 6.0.0 20160125 (experimental)"
.gnu_attribute 4, 1
.section.note.GNU-stack,"",@progbits

[Bug target/17381] Unnecessary register move for float extend

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17381

Andrew Pinski pinskia at gcc dot gnu.org changed:

   What|Removed |Added

 Status|ASSIGNED|NEW
 AssignedTo|pinskia at gcc dot gnu.org  |unassigned at gcc dot
   ||gnu.org

--- Comment #7 from Andrew Pinski pinskia at gcc dot gnu.org 2011-11-29 
23:20:48 UTC ---
No longer working on this though I will submit at least the regrename patch
soon.

[Bug target/17381] Unnecessary register move for float extend

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17381

--- Comment #6 from Andrew Pinski pinskia at gcc dot gnu.org 2011-01-05 
00:15:50 UTC ---
(In reply to comment #5)
 This is the patch which fixes the issue:Index: regrename.c
 ===
 --- regrename.c (revision 3023)
 +++ regrename.c (working copy)
 @@ -1374,6 +1374,10 @@ maybe_mode_change (enum machine_mode ori
enum machine_mode new_mode, unsigned int regno,
unsigned int copy_regno ATTRIBUTE_UNUSED)
  {
 +  if (GET_MODE_SIZE (copy_mode) == GET_MODE_SIZE (new_mode)
 +   hard_regno_nregs[copy_regno][copy_mode] ==
 hard_regno_nregs[copy_regno][new_mode]
 +   hard_regno_nregs[regno][copy_mode] ==
 hard_regno_nregs[copy_regno][new_mode])
 +return gen_rtx_raw_REG (new_mode, regno);
if (orig_mode == new_mode)
  return gen_rtx_raw_REG (new_mode, regno);
else if (mode_change_ok (orig_mode, new_mode, regno))

MIPS64 has a similar issue too, take:
long long d;
int test1(int fParm)
{
  d = fParm + 1;
  return fParm + 1;
}

The same regrename.c patch is needed to fix the MIPS64 issue too.

[Bug target/17381] Unnecessary register move for float extend

[pinskia at gcc dot gnu dot org]

--- Comment #5 from pinskia at gcc dot gnu dot org  2009-01-15 19:58 ---
This is the patch which fixes the issue:Index: regrename.c
===
--- regrename.c (revision 3023)
+++ regrename.c (working copy)
@@ -1374,6 +1374,10 @@ maybe_mode_change (enum machine_mode ori
   enum machine_mode new_mode, unsigned int regno,
   unsigned int copy_regno ATTRIBUTE_UNUSED)
 {
+  if (GET_MODE_SIZE (copy_mode) == GET_MODE_SIZE (new_mode)
+   hard_regno_nregs[copy_regno][copy_mode] ==
hard_regno_nregs[copy_regno][new_mode]
+   hard_regno_nregs[regno][copy_mode] ==
hard_regno_nregs[copy_regno][new_mode])
+return gen_rtx_raw_REG (new_mode, regno);
   if (orig_mode == new_mode)
 return gen_rtx_raw_REG (new_mode, regno);
   else if (mode_change_ok (orig_mode, new_mode, regno))
Index: config/rs6000/rs6000.md
===
--- config/rs6000/rs6000.md (revision 3023)
+++ config/rs6000/rs6000.md (working copy)
@@ -5247,10 +5247,17 @@ (define_insn_and_split *extendsfdf2_fpr
#
fmr %0,%1
lfs%U1%X1 %0,%1
-   reload_completed  REG_P (operands[1])  REGNO (operands[0]) == REGNO
(operands[1])
+   reload_completed  REG_P (operands[1])
   [(const_int 0)]
 {
-  emit_note (NOTE_INSN_DELETED);
+  if (REGNO (operands[0]) == REGNO (operands[1]))
+emit_note (NOTE_INSN_DELETED);
+  else
+{
+  rtx op0 = gen_rtx_REG (DFmode, REGNO (operands[0]));
+  rtx op1 = gen_rtx_REG (DFmode, REGNO (operands[1]));
+  emit_insn (gen_move_insn (op0, op1));
+}
   DONE;
 }
   [(set_attr type fp,fp,fpload)])


The rs6000 part is to tell the compiler what is really going on after register
allocator.  The regrename part allows to do a hard register copy propagation
after reload.
So we have:
(set (reg:SF 1) ... )
(set (reg:DF 2) (reg:DF 1))
(use (reg:DF 2))
After the rs6000.md patch.  Since the copy, is using the register in the larger
mode (DF), the last instruction should be just (use (reg:DF 1)).  This patch
allows for that.  


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17381

[Bug target/17381] Unnecessary register move for float extend

[pinskia at gcc dot gnu dot org]

--- Comment #4 from pinskia at gcc dot gnu dot org  2009-01-14 19:52 ---
I almost have a patch for this.


-- 

pinskia at gcc dot gnu dot org changed:

   What|Removed |Added

 AssignedTo|unassigned at gcc dot gnu   |pinskia at gcc dot gnu dot
   |dot org |org
 Status|NEW |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17381

[Bug target/17381] Unnecessary register move for float extend

[pinskia at gcc dot gnu dot org]

--- Comment #2 from pinskia at gcc dot gnu dot org  2005-12-18 02:10 ---
It is even worse with:
double d;
float test1(float fParm)
{
  d = fParm + 1.0;
  return fParm + 1.0f;
}

We get two extra fmr's and one extra load:
_test1:
fmr f12,f1   extra fmr
lis r2,ha16(LC1)
fmr f0,f1   extra fmr
lfs f13,lo16(LC1)(r2)  --- load of 1.0f
lfs f1,lo16(LC1)(r2)  --- load of 1.0f, extra load
lis r2,ha16(_d)
fadd f0,f0,f13
fadds f1,f12,f1
stfd f0,lo16(_d)(r2)
blr


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17381

[Bug target/17381] Unnecessary register move for float extend

[pinskia at gcc dot gnu dot org]

--- Comment #3 from pinskia at gcc dot gnu dot org  2005-12-18 02:37 ---
(In reply to comment #2)
 We get two extra fmr's and one extra load:
I filed the extra load as PR 25474.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17381