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[PATCH, i386]: Optimize TImode constant loads for x86_64
- From: Uros Bizjak <ubizjak at gmail dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 30 Jun 2008 23:24:08 +0200
- Subject: [PATCH, i386]: Optimize TImode constant loads for x86_64
Hello!
This patch optimizes TImode immediate operands to load directly from
memory to XMM register, while still generating "movabsq" insn when
loading immediate operand to TImode general register pair.
Currently, gcc compiles following test:
--cut here--
_Decimal128 test (void)
{
return 1234123412341234.123412341234dl;
}
--cut here--
to (-O2):
test:
movabsq $4404704354742567410, %rax
movabsq $3470023512955869132, %rdx
movq %rax, -24(%rsp)
movq %rdx, -16(%rsp)
movdqa -24(%rsp), %xmm0
ret
With attached patch, we generate:
test:
movdqa .LC0(%rip), %xmm0
ret
OTOH, for these testcases:
--cut here--
_Decimal128 a;
void tt (void)
{
a = 1234123412341234.123412341234dl;
}
__int128_t dd (int fd)
{
__int128_t x = 120986749876238ll;
return x + fd;
}
--cut here--
We still load constant to integer register pair:
tt:
movabsq $4404704354742567410, %rdx
movabsq $3470023512955869132, %rax
movq %rdx, a(%rip)
movq %rax, a+8(%rip)
ret
dd:
movslq %edi,%rdi
movabsq $120986749876238, %rcx
pushq %rbx
movq %rdi, %rax
movq %rdi, %rdx
xorl %ebx, %ebx
sarq $63, %rdx
addq %rcx, %rax
adcq %rbx, %rdx
popq %rbx
ret
2008-06-30 Uros Bizjak <ubizjak@gmail.com>
* config/i386/i386.md (*movti_rex64): Add "!" to "r" constraint
of operand 0.
testsuite/ChangeLog:
2008-06-30 Uros Bizjak <ubizjak@gmail.com>
* gcc.target/i386/movti.c: New test.
Patch was bootstrapped and regression tested on x86_64-pc-linux-gnu.
Patch is committed to mainline.
Uros.
Index: config/i386/i386.md
===================================================================
--- config/i386/i386.md (revision 137276)
+++ config/i386/i386.md (working copy)
@@ -2464,7 +2464,7 @@
(const_string "TI")))])
(define_insn "*movti_rex64"
- [(set (match_operand:TI 0 "nonimmediate_operand" "=r,o,x,x,xm")
+ [(set (match_operand:TI 0 "nonimmediate_operand" "=!r,o,x,x,xm")
(match_operand:TI 1 "general_operand" "riFo,riF,C,xm,x"))]
"TARGET_64BIT
&& !(MEM_P (operands[0]) && MEM_P (operands[1]))"
Index: testsuite/gcc.target/i386/movti.c
===================================================================
--- testsuite/gcc.target/i386/movti.c (revision 0)
+++ testsuite/gcc.target/i386/movti.c (revision 0)
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target dfp } */
+/* { dg-options "-O -std=gnu99" } */
+
+_Decimal128 test (void)
+{
+ return 1234123412341234.123412341234dl;
+}
+
+/* { dg-final { scan-assembler-not "movabs" } } */