Hi!
Doing a movl + shlq by constant seems to be 1 byte shorter
than movabsq, so this patch attempts to use the former form
unless flags is live.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Performance-wise, not really sure what is a win (on i7-5960X on the
testcase in the PR movl + shlq seems to be significantly faster, but e.g.
on i7-2600 it is the same) so not doing anything for speed yet.
2017-09-27 Jakub Jelinek <ja...@redhat.com>
PR target/82339
* config/i386/i386.md (*movdi_internal peephole2): New -Os peephole
for movabsq $(i32 << shift), r64.
--- gcc/config/i386/i386.md.jj 2017-09-21 09:26:42.000000000 +0200
+++ gcc/config/i386/i386.md 2017-09-27 10:24:01.520673889 +0200
@@ -2379,6 +2379,28 @@ (define_split
gen_lowpart (SImode, operands[1]));
})
+;; movabsq $0x0012345678000000, %rax is longer
+;; than movl $0x12345678, %eax; shlq $24, %rax.
+(define_peephole2
+ [(set (match_operand:DI 0 "register_operand")
+ (match_operand:DI 1 "const_int_operand"))]
+ "TARGET_64BIT
+ && optimize_insn_for_size_p ()
+ && LEGACY_INT_REG_P (operands[0])
+ && !x86_64_immediate_operand (operands[1], DImode)
+ && !x86_64_zext_immediate_operand (operands[1], DImode)
+ && !((UINTVAL (operands[1]) >> ctz_hwi (UINTVAL (operands[1])))
+ & ~(HOST_WIDE_INT) 0xffffffff)
+ && peep2_regno_dead_p (0, FLAGS_REG)"
+ [(set (match_dup 0) (match_dup 1))
+ (parallel [(set (match_dup 0) (ashift:DI (match_dup 0) (match_dup 2)))
+ (clobber (reg:CC FLAGS_REG))])]
+{
+ int shift = ctz_hwi (UINTVAL (operands[1]));
+ operands[1] = gen_int_mode (UINTVAL (operands[1]) >> shift, DImode);
+ operands[2] = gen_int_mode (shift, QImode);
+})
+
(define_insn "*movsi_internal"
[(set (match_operand:SI 0 "nonimmediate_operand"
"=r,m ,*y,*y,?*y,?m,?r ,?*Ym,*v,*v,*v,m ,?r ,?*Yi,*k,*k ,*rm")
Jakub
