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291 Commits

Author SHA1 Message Date
Benjamin Kramer
162ee5c725 Add a neat little two's complement hack for x86. 
On x86 we can't encode an immediate LHS of a sub directly. If the RHS comes from a XOR with a constant we can
fold the negation into the xor and add one to the immediate of the sub. Then we can turn the sub into an add,
which can be commuted and encoded efficiently.

This code is generated for __builtin_clz and friends.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@136167 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-07-26 22:42:13 +00:00
Benjamin Kramer
a3d782f40c Add a note about efficient codegen for binary log. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@135996 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-07-25 22:30:00 +00:00
Chris Lattner
5d4718b1c7 add a note 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131455 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-05-17 07:22:33 +00:00
Benjamin Kramer
ce3a022b8c This is done. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130499 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-04-29 14:09:57 +00:00
Chris Lattner
4c19b17a17 move PR9803 to this readme. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130385 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-04-28 05:33:16 +00:00
Eli Friedman
2f108f81c1 Remove working entry from README. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129654 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-04-17 02:36:27 +00:00
Chris Lattner
7a2bdde0a0 Fix a ton of comment typos found by codespell. Patch by 
Luis Felipe Strano Moraes!



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129558 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-04-15 05:18:47 +00:00
Chris Lattner
b8295f7a0e move PR9661 out to here. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129527 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-04-14 18:47:18 +00:00
Rafael Espindola
3d195faaad Add another case we are not optimizing. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129012 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-04-06 17:35:32 +00:00
Rafael Espindola
8617897aaa The original issue has been fixed by not doing unnecessary sign extensions. 
Change the test to force a sign extension and expose the problem again.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129011 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-04-06 17:19:35 +00:00
Eli Friedman
3d831381a9 A couple new README entries. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127786 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-03-17 01:22:09 +00:00
Chris Lattner
fb456c25c2 a serious "compare CSE" issue that is nontrivial to get right, 
but which is responsible for us doing really bad things to 256.bzip2.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126126 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-02-21 17:03:47 +00:00
Cameron Zwarich
ad48a4fc32 A lo/hi mul has higher latency than an imul r,ri, e.g. 5 cycles compared to 3 
on Core 2 and Nehalem, so the code we generate is better than GCC's here.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126100 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-02-21 01:29:32 +00:00
Cameron Zwarich
8d7285d0e5 The signed version of our "magic number" computation for the integer approximation 
of a constant had a minor typo introduced when copying it from the book, which
caused it to favor negative approximations over positive approximations in many
cases. Positive approximations require fewer operations beyond the multiplication.

In the case of division by 3, we still generate code that is a single instruction
larger than GCC's code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126097 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-02-21 00:22:02 +00:00
Eli Friedman
86b115c78b Minor x86 README updates. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126054 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-02-19 21:54:28 +00:00
Chris Lattner
c1e4ce6044 add a poor division by constant case. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125832 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-02-18 05:35:49 +00:00
Chris Lattner
527b47d189 update a bunch of entries. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122700 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-01-02 18:31:38 +00:00
Chris Lattner
6dbb5dc5eb fix some sort of weird pasto 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122560 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-12-26 12:05:11 +00:00
Chris Lattner
8a4893e013 add a note 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122559 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-12-26 03:53:31 +00:00
Benjamin Kramer
3e4106105b Remove some obsolete README items, add a new one off the top of my head. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122495 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-12-23 15:07:02 +00:00
Benjamin Kramer
e915ff30cd X86: Lower a select directly to a setcc_carry if possible. 
int test(unsigned long a, unsigned long b) { return -(a < b); }
compiles to
  _test:                              ## @test
    cmpq  %rsi, %rdi                  ## encoding: [0x48,0x39,0xf7]
    sbbl  %eax, %eax                  ## encoding: [0x19,0xc0]
    ret                               ## encoding: [0xc3]
instead of
  _test:                              ## @test
    xorl  %ecx, %ecx                  ## encoding: [0x31,0xc9]
    cmpq  %rsi, %rdi                  ## encoding: [0x48,0x39,0xf7]
    movl  $-1, %eax                   ## encoding: [0xb8,0xff,0xff,0xff,0xff]
    cmovael %ecx, %eax                ## encoding: [0x0f,0x43,0xc1]
    ret                               ## encoding: [0xc3]


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122451 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-12-22 23:09:28 +00:00
Benjamin Kramer
20e3b4b380 Factor the (x & 2^n) ? 2^m : 0 instcombine into its own method and generalize it 
to catch cases where n != m with a shift.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121608 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-12-11 09:42:59 +00:00
Evan Cheng
3d2125c9db Enable sibling call optimization of libcalls which are expanded during 
legalization time. Since at legalization time there is no mapping from
SDNode back to the corresponding LLVM instruction and the return
SDNode is target specific, this requires a target hook to check for
eligibility. Only x86 and ARM support this form of sibcall optimization
right now.
rdar://8707777


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120501 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-11-30 23:55:39 +00:00
Chris Lattner
8bc1e45295 apparently tailcalls are better on darwin/x86-64 than on linux? 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119947 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-11-21 18:59:20 +00:00
Dan Gohman
24bde5bce1 Don't narrow the load and store in a load+twiddle+store sequence unless 
there are clearly no stores between the load and the store. This fixes
this miscompile reported as PR7833.

This breaks the test/CodeGen/X86/narrow_op-2.ll optimization, which is
safe, but awkward to prove safe. Move it to X86's README.txt.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112861 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-09-02 21:18:42 +00:00
Eli Friedman
5033f64694 A couple of small missed optimizations. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112411 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-08-29 05:07:40 +00:00
Eric Christopher
9a9d275dc7 Custom lower the memory barrier instructions and add support 
for lowering without sse2.  Add a couple of new testcases.

Fixes a few libgomp tests and latent bugs.  Remove a few todos.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@109078 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-07-22 02:48:34 +00:00
Eli Friedman
2ad7e433c9 Remove a fixed item, update a couple partially-fixed items. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@105375 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-06-03 01:01:48 +00:00
Dan Gohman
85e9601862 This is now done. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97450 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-03-01 17:43:57 +00:00
Eli Friedman
11d91e80b4 A few missed optimizations; the last one could have a significant impact on 
code with lots of bitfields.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95809 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-02-10 21:26:04 +00:00
Chris Lattner
5350f78323 this is an SSE-specific issue. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93373 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-01-13 23:29:11 +00:00
Chris Lattner
689339c50f X86 if conversion + tail merging issues from PR6032. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93372 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-01-13 23:28:40 +00:00
Dan Gohman
3c02c22ef9 Remove some README.txt entries which are now implemented. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92511 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-01-04 20:55:05 +00:00
Eli Friedman
1f1b0f748d A couple minor README updates. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91823 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-12-21 08:03:16 +00:00
Bill Wendling
5a56927345 Move and clarify note. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85334 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-10-27 22:48:31 +00:00
Bill Wendling
de020736c0 Note corrected. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85332 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-10-27 22:43:24 +00:00
Bill Wendling
d8499c9b7f Modify note. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85331 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-10-27 22:40:45 +00:00
Bill Wendling
1ff2c485e2 Add a note. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85329 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-10-27 22:34:43 +00:00
Evan Cheng
7216920791 Add a note. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77584 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-07-30 08:56:19 +00:00
Chris Lattner
e3821c79bc remove a bogus note. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74509 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-06-30 05:22:31 +00:00
Chris Lattner
a05ec61684 add a note 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74508 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-06-30 04:20:46 +00:00
Chris Lattner
b42e20be77 another xform that is target-independent (should be done in instcombine). 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73472 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-06-16 06:15:56 +00:00
Chris Lattner
d23fffeb16 I think instcombine should unconditionally do this xform. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73471 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-06-16 06:11:35 +00:00
Eli Friedman
7161cb1dad Misc x86 README updates: remove a couple of already-fixed issues, 
add a few suggestions from looking at some assembly code.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73210 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-06-11 23:07:04 +00:00
Chris Lattner
d9b77159d6 add some late optimizations that GCC does. It thinks these are a win 
even on Core2, not just AMD processors which was a surprise to me.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72396 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-05-25 20:28:19 +00:00
Chris Lattner
f9dc644936 we should eventually add -march=atom and the new atom movbe instruction. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72387 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-05-25 16:34:44 +00:00
Chris Lattner
d1980a5acd Move 3 "(add (select cc, 0, c), x) -> (select cc, x, (add, x, c))" 
related transformations out of target-specific dag combine into the
ARM backend.  These were added by Evan in r37685 with no testcases
and only seems to help ARM (e.g. test/CodeGen/ARM/select_xform.ll).

Add some simple X86-specific (for now) DAG combines that turn things
like cond ? 8 : 0  -> (zext(cond) << 3).  This happens frequently
with the recently added cp constant select optimization, but is a
very general xform.  For example, we now compile the second example
in const-select.ll to:

_test:
        movsd   LCPI2_0, %xmm0
        ucomisd 8(%esp), %xmm0
        seta    %al
        movzbl  %al, %eax
        movl    4(%esp), %ecx
        movsbl  (%ecx,%eax,4), %eax
        ret

instead of:

_test:
        movl    4(%esp), %eax
        leal    4(%eax), %ecx
        movsd   LCPI2_0, %xmm0
        ucomisd 8(%esp), %xmm0
        cmovbe  %eax, %ecx
        movsbl  (%ecx), %eax
        ret

This passes multisource and dejagnu.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66779 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-03-12 06:52:53 +00:00
Dan Gohman
3328adda6b Add more information to the EFLAGS note. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66515 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-03-10 00:26:23 +00:00
Dan Gohman
ad93e1e5fc Add a note about EFLAGS optimization. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66508 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-03-09 23:47:02 +00:00
Chris Lattner
ff9dcee534 add a note. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66360 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-03-08 03:04:26 +00:00