Commit Graph

8 Commits

Author SHA1 Message Date
Hal Finkel 8adf2254ef [PowerPC] Improve instruction selection bit-permuting operations (32-bit)
The PowerPC backend, somewhat embarrassingly, did not generate an
optimal-length sequence of instructions for a 32-bit bswap. While adding a
pattern for the bswap intrinsic to fix this would not have been terribly
difficult, doing so would not have addressed the real problem: we had been
generating poor code for many bit-permuting operations (by which I mean things
like byte-swap that permute the bits of one or more inputs around in various
ways). Here are some initial steps toward solving this deficiency.

Bit-permuting operations are represented, at the SDAG level, using ISD::ROTL,
SHL, SRL, AND and OR (mostly with constant second operands). Looking back
through these operations, we can build up a description of the bits in the
resulting value in terms of bits of one or more input values (and constant
zeros). For each bit, we compute the rotation amount from the original value,
and then group consecutive (value, rotation factor) bits into groups. Groups
sharing these attributes are then collected and sorted, and we can then
instruction select the entire permutation using a combination of masked
rotations (rlwinm), imm ands (andi/andis), and masked rotation inserts
(rlwimi).

The result is that instead of lowering an i32 bswap as:

	rlwinm 5, 3, 24, 16, 23
	rlwinm 4, 3, 24, 0, 7
	rlwimi 4, 3, 8, 8, 15
	rlwimi 5, 3, 8, 24, 31
	rlwimi 4, 5, 0, 16, 31

we now produce:

	rlwinm 4, 3, 8, 0, 31
	rlwimi 4, 3, 24, 16, 23
	rlwimi 4, 3, 24, 0, 7

and for the 'test6' example in the PowerPC/README.txt file:

 unsigned test6(unsigned x) {
   return ((x & 0x00FF0000) >> 16) | ((x & 0x000000FF) << 16);
 }

we used to produce:

	lis 4, 255
	rlwinm 3, 3, 16, 0, 31
	ori 4, 4, 255
	and 3, 3, 4

and now we produce:

	rlwinm 4, 3, 16, 24, 31
	rlwimi 4, 3, 16, 8, 15

and, as a nice bonus, this fixes the FIXME in
test/CodeGen/PowerPC/rlwimi-and.ll.

This commit does not include instruction-selection for i64 operations, those
will come later.

llvm-svn: 224318
2014-12-16 05:51:41 +00:00
Chris Lattner 295097cc32 add some nounwind's.
llvm-svn: 119086
2010-11-14 22:22:14 +00:00
Dan Gohman c8054d90fb Eliminate more uses of llvm-as and llvm-dis.
llvm-svn: 81293
2009-09-09 00:09:15 +00:00
Dan Gohman 0d4bbf2c4a Remove obsolete -f flags.
llvm-svn: 79992
2009-08-25 15:38:29 +00:00
Tanya Lattner a99d8b5a9a Remove llvm-upgrade and update tests.
llvm-svn: 47325
2008-02-19 08:07:33 +00:00
Dan Gohman f9dd170e36 Convert tests using "| wc -l | grep ..." to use the count script.
llvm-svn: 41097
2007-08-15 13:36:28 +00:00
Reid Spencer 6e87ec4351 For PR1319:
Remove && from the end of the lines to prevent tests from throwing run
lines into the background. Also, clean up places where the same command
is run multiple times by using a temporary file.

llvm-svn: 36142
2007-04-16 17:36:08 +00:00
Reid Spencer 83b3d82672 Regression is gone, don't try to find it on clean target.
llvm-svn: 33296
2007-01-17 07:59:14 +00:00