llvm-project

Commit Graph

Author	SHA1	Message	Date
Sanjay Patel	203fd23d6e	specify triple so Windows bots won't be sad llvm-svn: 252519	2015-11-09 21:53:58 +00:00
Sanjay Patel	32538d6811	[x86] try harder to match bitwise 'or' into an LEA The motivation for this patch starts with the epic fail example in PR18007: https://llvm.org/bugs/show_bug.cgi?id=18007 ...unfortunately, this patch makes no difference for that case, but it solves some simpler cases. We'll get there some day. :) The current 'or' matching code was using computeKnownBits() via isBaseWithConstantOffset() -> MaskedValueIsZero(), but that's an unnecessarily limited use. We can do more by copying the logic in ValueTracking's haveNoCommonBitsSet(), so we can treat the 'or' as if it was an 'add'. There's a TODO comment here because we should lift the bit-checking logic into a helper function, so it's not duplicated in DAGCombiner. An example of the better LEA matching: leal (%rdi,%rdi), %eax andl $1, %esi orl %esi, %eax Becomes: andl $1, %esi leal (%rsi,%rdi,2), %eax Differential Revision: http://reviews.llvm.org/D13956 llvm-svn: 252515	2015-11-09 21:16:49 +00:00
Ekaterina Romanova	d5fa55470c	SHLD/SHRD are VectorPath (microcode) instructions known to have poor latency on certain architectures. While generating SHLD/SHRD instructions is acceptable when optimizing for size, optimizing for speed on these platforms should be implemented using alternative sequences of instructions composed of add, adc, shr, shl, or and lea which are directPath instructions. These alternative instructions not only have a lower latency but they also increase the decode bandwidth by allowing simultaneous decoding of a third directPath instruction. AMD's processors family K7, K8, K10, K12, K15 and K16 are known to have SHLD/SHRD instructions with very poor latency. Optimization guides for these processors recommend using an alternative sequence of instructions. For these AMD's processors, I disabled folding (or (x << c) \| (y >> (64 - c))) when we are not optimizing for size. It might be beneficial to disable this folding for some of the Intel's processors. However, since I couldn't find specific recommendations regarding using SHLD/SHRD instructions on Intel's processors, I haven't disabled this peephole for Intel. llvm-svn: 195383	2013-11-21 23:21:26 +00:00

Author

SHA1

Message

Date

Sanjay Patel

203fd23d6e

specify triple so Windows bots won't be sad

llvm-svn: 252519

2015-11-09 21:53:58 +00:00

Sanjay Patel

32538d6811

[x86] try harder to match bitwise 'or' into an LEA

The motivation for this patch starts with the epic fail example in PR18007:
https://llvm.org/bugs/show_bug.cgi?id=18007

...unfortunately, this patch makes no difference for that case, but it solves some
simpler cases. We'll get there some day. :)

The current 'or' matching code was using computeKnownBits() via 
isBaseWithConstantOffset() -> MaskedValueIsZero(), but that's an unnecessarily limited use. 
We can do more by copying the logic in ValueTracking's haveNoCommonBitsSet(), so we can 
treat the 'or' as if it was an 'add'.

There's a TODO comment here because we should lift the bit-checking logic into a helper
function, so it's not duplicated in DAGCombiner.

An example of the better LEA matching:

leal (%rdi,%rdi), %eax
andl $1, %esi
orl %esi, %eax

Becomes:

andl $1, %esi
leal (%rsi,%rdi,2), %eax

Differential Revision: http://reviews.llvm.org/D13956

llvm-svn: 252515

2015-11-09 21:16:49 +00:00

Ekaterina Romanova

d5fa55470c

SHLD/SHRD are VectorPath (microcode) instructions known to have poor latency on certain architectures. While generating SHLD/SHRD instructions is acceptable when optimizing for size, optimizing for speed on these platforms should be implemented using alternative sequences of instructions composed of add, adc, shr, shl, or and lea which are directPath instructions. These alternative instructions not only have a lower latency but they also increase the decode bandwidth by allowing simultaneous decoding of a third directPath instruction.

AMD's processors family K7, K8, K10, K12, K15 and K16 are known to have SHLD/SHRD instructions with very poor latency. Optimization guides for these processors recommend using an alternative sequence of instructions. For these AMD's processors, I disabled folding (or (x << c) | (y >> (64 - c))) when we are not optimizing for size.

It might be beneficial to disable this folding for some of the Intel's processors. However, since I couldn't find specific recommendations regarding using SHLD/SHRD instructions on Intel's processors, I haven't disabled this peephole for Intel.

llvm-svn: 195383

2013-11-21 23:21:26 +00:00

3 Commits