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274 Commits

Author SHA1 Message Date
Benjamin Kramer 2e63f6eac0 Add two notes for correlated-expression optimizations. 
llvm-svn: 139263
 2011-09-07 22:49:26 +00:00
Benjamin Kramer 15cd5a3f12 Don't emit a bit test if there is only one case the test can yield false. A simple SETNE is sufficient. 
llvm-svn: 135126
 2011-07-14 01:38:42 +00:00
Benjamin Kramer c970849ea0 InstCombine: Fold A-b == C --> b == A-C if A and C are constants. 
The backend already knew this trick.

llvm-svn: 132915
 2011-06-13 15:24:24 +00:00
Chris Lattner d71ed9431a clarify this, apparently it is confusing :) 
llvm-svn: 131916
 2011-05-23 20:17:44 +00:00
Chris Lattner bfe2c24c80 add a note. 
llvm-svn: 131863
 2011-05-22 18:28:46 +00:00
Chris Lattner bbc40ac474 move PR9408 here. 
llvm-svn: 131841
 2011-05-22 05:45:06 +00:00
Chris Lattner 1b06c71668 Transform: "icmp eq (trunc (lshr(X, cst1)), cst" to "icmp (and X, mask), cst" 
when X has multiple uses.  This is useful for exposing secondary optimizations,
but the X86 backend isn't ready for this when X has a single use.  For example,
this can disable load folding.

This is inching towards resolving PR6627.

llvm-svn: 130238
 2011-04-26 20:18:20 +00:00
Chris Lattner 6e29892430 add a missed bitfield instcombine. 
llvm-svn: 130137
 2011-04-25 18:44:26 +00:00
Benjamin Kramer 341c11da3b DAGCombine: fold "(zext x) == C" into "x == (trunc C)" if the trunc is lossless. 
On x86 this allows to fold a load into the cmp, greatly reducing register pressure.
  movzbl	(%rdi), %eax
  cmpl	$47, %eax
->
  cmpb	$47, (%rdi)

This shaves 8k off gcc.o on i386. I'll leave applying the patch in README.txt to Chris :)

llvm-svn: 130005
 2011-04-22 18:47:44 +00:00
Chris Lattner 1d313c6f6d add a minor missed dag combine that is blocking mid-level optimization 
improvements, that will lead to fixing PR6627.

llvm-svn: 129504
 2011-04-14 04:21:42 +00:00
Benjamin Kramer dc0082b087 Add a note. 
llvm-svn: 128286
 2011-03-25 17:32:40 +00:00
Eli Friedman 822e7bc061 A bit more analysis of a memset-related README entry. 
llvm-svn: 128107
 2011-03-22 20:49:53 +00:00
Eli Friedman 8e15a661bf This README entry was fixed recently. 
llvm-svn: 127982
 2011-03-21 01:33:03 +00:00
Chris Lattner 0c6cb46ac1 add a note 
llvm-svn: 126719
 2011-03-01 00:24:51 +00:00
Benjamin Kramer 26691d9660 Add some DAGCombines for (adde 0, 0, glue), which are useful to optimize legalized code for large integer arithmetic. 
1. Inform users of ADDEs with two 0 operands that it never sets carry
2. Fold other ADDs or ADDCs into the ADDE if possible

It would be neat if we could do the same thing for SETCC+ADD eventually, but we can't do that in target independent code.

llvm-svn: 126557
 2011-02-26 22:48:07 +00:00
Chris Lattner e9cba7bd34 add a missed loop deletion case. 
llvm-svn: 126103
 2011-02-21 02:13:39 +00:00
Chris Lattner 659c793a4e add an idiom that loop idiom could theoretically catch. 
llvm-svn: 126101
 2011-02-21 01:33:38 +00:00
Duncan Sands 491eb276a7 This has been implemented. 
llvm-svn: 125738
 2011-02-17 08:16:56 +00:00
Chris Lattner 727eebee58 add some notes on compares + binops. Remove redundant entries. 
llvm-svn: 125702
 2011-02-17 01:43:46 +00:00
Chris Lattner 28bf91f78e Add a few missed xforms from GCC PR14753 
llvm-svn: 125681
 2011-02-16 19:16:34 +00:00
Eli Friedman c8fb2557b9 Remove outdated README entry. 
llvm-svn: 125660
 2011-02-16 07:41:19 +00:00
Eli Friedman 0254c4c01b Remove outdated README entry. 
llvm-svn: 125659
 2011-02-16 07:18:18 +00:00
Eli Friedman 5f75515e5d Update README entry. 
llvm-svn: 125658
 2011-02-16 07:17:44 +00:00
Anders Carlsson 49d81a3d7e Remove a virtual inheritance case that clang can devirtualize fully now. 
llvm-svn: 124989
 2011-02-06 20:16:49 +00:00
Benjamin Kramer f4ea1d5f79 SimplifyCFG: Turn switches into sub+icmp+branch if possible. 
This makes the job of the later optzn passes easier, allowing the vast amount of
icmp transforms to chew on it.

We transform 840 switches in gcc.c, leading to a 16k byte shrink of the resulting
binary on i386-linux.

The testcase from README.txt now compiles into
  decl  %edi
  cmpl  $3, %edi
  sbbl  %eax, %eax
  andl  $1, %eax
  ret

llvm-svn: 124724
 2011-02-02 15:56:22 +00:00
Chris Lattner 865fe3b283 add a note, progress unblocked by PR8575 being fixed. 
llvm-svn: 124599
 2011-01-31 20:23:28 +00:00
Benjamin Kramer 946e1522b6 Teach DAGCombine to fold fold (sra (trunc (sr x, c1)), c2) -> (trunc (sra x, c1+c2) when c1 equals the amount of bits that are truncated off. 
This happens all the time when a smul is promoted to a larger type.

On x86-64 we now compile "int test(int x) { return x/10; }" into
  movslq  %edi, %rax
  imulq $1717986919, %rax, %rax
  movq  %rax, %rcx
  shrq  $63, %rcx
  sarq  $34, %rax <- used to be "shrq $32, %rax; sarl $2, %eax"
  addl  %ecx, %eax

This fires 96 times in gcc.c on x86-64.

llvm-svn: 124559
 2011-01-30 16:38:43 +00:00
Chris Lattner 9685603260 this isn't a memset, we do convert dest[i] to one though :) 
llvm-svn: 124097
 2011-01-24 02:32:00 +00:00
Chris Lattner b830ee5250 with recent work, we now optimize this into: 
define i32 @foo(i32 %x) nounwind readnone ssp {
entry:
  %tobool = icmp eq i32 %x, 0
  %tmp5 = select i1 %tobool, i32 2, i32 1
  ret i32 %tmp5
}

llvm-svn: 124091
 2011-01-24 01:12:18 +00:00
Anders Carlsson 773bc67eff Add a memset loop that LoopIdiomRecognize doesn't recognize. 
llvm-svn: 124082
 2011-01-23 20:31:00 +00:00
Chris Lattner a56c8279e8 add a note 
llvm-svn: 123752
 2011-01-18 07:47:48 +00:00
Anders Carlsson 6a5171ba68 Update README.txt to remove the DAE enhancement. 
llvm-svn: 123597
 2011-01-16 21:26:15 +00:00
Chris Lattner c326ebd118 add some commentary 
llvm-svn: 123572
 2011-01-16 06:39:44 +00:00
Chandler Carruth ef28abefd0 Simplify a README.txt entry significantly to expose the core issue. 
llvm-svn: 123556
 2011-01-16 01:40:23 +00:00
Chris Lattner b6c3aff1cb typo 
llvm-svn: 123406
 2011-01-13 22:11:56 +00:00
Chris Lattner b9cdf393a4 memcpy + metadata = bliss :) 
llvm-svn: 123405
 2011-01-13 22:08:15 +00:00
Chandler Carruth b1e7f557b7 Teach constant folding to perform conversions from constant floating 
point values to their integer representation through the SSE intrinsic
calls. This is the last part of a README.txt entry for which I have real
world examples.

llvm-svn: 123206
 2011-01-11 01:07:24 +00:00
Owen Anderson d490c2d2ae Fix a random missed optimization by making InstCombine more aggressive when determining which bits are demanded by 
a comparison against a constant.

llvm-svn: 123203
 2011-01-11 00:36:45 +00:00
Chris Lattner 78cdd2a6c6 +0.0 vs -0.0 differences can be handled by looking at the user of the 
operation in some cases.

llvm-svn: 123190
 2011-01-10 21:01:17 +00:00
Chris Lattner eef1455020 expand on a note 
llvm-svn: 123145
 2011-01-10 00:33:01 +00:00
Chris Lattner 5b358c6825 typo 
llvm-svn: 123142
 2011-01-09 23:48:41 +00:00
Chris Lattner 320370e3ca xref a PR # 
llvm-svn: 123141
 2011-01-09 23:42:22 +00:00
Chandler Carruth d011d5317c Add a note about the inability to model FP -> int conversions which 
perform rounding other than truncation in the IR. Common C code for this
turns into really an LLVM intrinsic call that blocks a lot of further
optimizations.

llvm-svn: 123135
 2011-01-09 22:36:18 +00:00
Chandler Carruth 0c68a668fa Add a note about a missed FP optimization. 
llvm-svn: 123126
 2011-01-09 21:00:19 +00:00
Chandler Carruth 82e6f6a325 Another missed memset in std::vector initialization. 
llvm-svn: 123116
 2011-01-09 11:29:57 +00:00
Chandler Carruth 43f6d1b67e Fix a cut-paste-o so that the sample code is correct for my last note. 
Also, switch to a more clear 'sink' function with its declaration to
avoid any confusion about 'g'. Thanks for the suggestion Frits.

llvm-svn: 123113
 2011-01-09 10:10:59 +00:00
Chandler Carruth ad6e1f0501 Another missed optimization of trivial vector code. 
llvm-svn: 123112
 2011-01-09 09:58:36 +00:00
Chandler Carruth f32619300a Add a note about vector's size-constructor producing dead stores. 
llvm-svn: 123111
 2011-01-09 09:58:33 +00:00
Chandler Carruth 5d684c17a7 Add a note about a missed memset optimization from std::fill. 
llvm-svn: 123103
 2011-01-09 01:32:55 +00:00
Benjamin Kramer 134cde912a Revert 122959, it needs more thought. Add it back to README.txt with additional notes. 
llvm-svn: 123030
 2011-01-07 20:42:20 +00:00