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[Bug target/54429] New: [SH] SImode values get ferried through FPUL and FP regs for -O0
- From: "olegendo at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 30 Aug 2012 22:26:40 +0000
- Subject: [Bug target/54429] New: [SH] SImode values get ferried through FPUL and FP regs for -O0
- Auto-submitted: auto-generated
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54429
Bug #: 54429
Summary: [SH] SImode values get ferried through FPUL and FP
regs for -O0
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: target
AssignedTo: olegendo@gcc.gnu.org
ReportedBy: olegendo@gcc.gnu.org
CC: kkojima@gcc.gnu.org
Target: sh*-*-*
I've noticed that, for some reason, when compiling code with -O0 SImode values
get ferried through FPUL reg and FP regs, like ..
lds r1,fpul
fsts fpul,fr1
mov r7,r4
flds fr1,fpul
sts fpul,r5
.. which is really just:
mov r1,r5
mov r7,r4
In sh_hard_regno_mode_ok, I've tried doing:
Index: gcc/config/sh/sh.c
===================================================================
--- gcc/config/sh/sh.c (revision 190780)
+++ gcc/config/sh/sh.c (working copy)
@@ -11706,6 +11706,9 @@
if (FP_REGISTER_P (regno) && mode == SFmode)
return true;
+ if (FP_REGISTER_P (regno) && GET_MODE_CLASS (mode) != MODE_FLOAT)
+ return false;
+
if (mode == V2SFmode)
{
if (((FP_REGISTER_P (regno) && (regno - FIRST_FP_REG) % 2 == 0)
.. and it makes the confusing FP reg usage go away. Somehow, I don't
understand why it would make sense to allow any integer modes in FP regs on SH.
No useful integer operations can be done with integer values in FP regs
anyway. The only purpose that I see, is to allow spilling of GP regs to FP
regs, which doesn't seem beneficial.
I've checked CSiBE results with the fix above. It causes a few increases and
decreases in the teem lib. The increases are, because GP regs are not spilled
to FP regs anymore and have to go to the stack, which causes some unlucky
displacement address changes. The decreases are because of the same, but where
displacement addresses are lucky. Also, weird cases disappear where FP regs
are pushed/popped in a function but are otherwise unused.
Kaz, do you happen to know why the sh_hard_regno_mode_ok function is the way it
is? I think The FP reg check after the V16SFmode check ...
if (FP_REGISTER_P (regno))
{
if (mode == SFmode
|| mode == SImode
....
would also become obsolete if the change above was applied?