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(EXT_SHIFT_SIGNED): New macro. 

(shl_sext_kind, gen_shl_sext): try left shift - sign extend -
left shift - arithmetic right shift in case 2.

From-SVN: r13059
This commit is contained in:
Joern Rennecke 1996-10-29 01:08:53 +00:00
parent 0f13a42202
commit ae9d19c0e1
1 changed files with 27 additions and 10 deletions
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37
gcc/config/sh/sh.c
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@ -701,6 +701,11 @@ static short ext_shift_amounts[32][4] = {
{16, 8}, {16, 1, 8}, {16, 8, 2}, {16, 8, 1, 2},
{16, 8, 2, 2}, {16, -1, -2, 16}, {16, -2, 16}, {16, -1, 16}};
/* Assuming we have a value that has been sign-extended by at least one bit,
can we use the ext_shift_amounts with the last shift turned to an arithmetic shift
to shift it by N without data loss, and quicker than by other means? */
#define EXT_SHIFT_SIGNED(n) (((n) | 8) == 15)
/* This is used in length attributes in sh.md to help compute the length
of arbitrary constant shift instructions. */
@ -1372,17 +1377,21 @@ shl_sext_kind (left_rtx, size_rtx, costp)
best_cost = cost;
}
}
if (size <= 16)
/* Check if we can do a sloppy shift with a final signed shift
restoring the sign. */
if (EXT_SHIFT_SIGNED (size - ext))
cost = ext_shift_insns[ext - insize] + ext_shift_insns[size - ext] + 1;
/* If not, maybe it's still cheaper to do the second shift sloppy,
and do a final sign extend? */
else if (size <= 16)
cost = ext_shift_insns[ext - insize] + 1
+ ext_shift_insns[size > ext ? size - ext : ext - size] + 1;
else
continue;
if (cost < best_cost)
{
/* Maybe it's cheaper to do the second shift sloppy, and do a
final sign extend? */
cost = ext_shift_insns[ext - insize] + 1
+ ext_shift_insns[size > ext ? size - ext : ext - size] + 1;
if (cost < best_cost)
{
kind = ext / 8U + 2;
best_cost = cost;
}
kind = ext / 8U + 2;
best_cost = cost;
}
}
/* Check if we can sign extend in r0 */
@ -1493,6 +1502,14 @@ gen_shl_sext (dest, left_rtx, size_rtx, source)
{
if (shift2 > 0)
{
if (EXT_SHIFT_SIGNED (shift2))
{
operands[2] = GEN_INT (shift2 + 1);
gen_shifty_op (ASHIFT, operands);
operands[2] = GEN_INT (1);
gen_shifty_op (ASHIFTRT, operands);
break;
}
operands[2] = GEN_INT (shift2);
gen_shifty_hi_op (ASHIFT, operands);
}