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Author SHA1 Message Date
Roman Lebedev 68d54cf5b3 [InstCombine] Fold x & (-1 >> y) == x to x u<= (-1 >> y) 
Summary:
https://bugs.llvm.org/show_bug.cgi?id=38123

This pattern will be produced by Implicit Integer Truncation sanitizer,
https://reviews.llvm.org/D48958
https://bugs.llvm.org/show_bug.cgi?id=21530
in unsigned case, therefore it is probably a good idea to improve it.

https://rise4fun.com/Alive/Rny
^ there are more opportunities for folds, i will follow up with them afterwards.

Caveat: this somehow exposes a missing opportunities
in `test/Transforms/InstCombine/icmp-logical.ll`
It seems, the problem is in `foldLogOpOfMaskedICmps()` in `InstCombineAndOrXor.cpp`.
But i'm not quite sure what is wrong, because it calls `getMaskedTypeForICmpPair()`,
which calls `decomposeBitTestICmp()` which should already work for these cases...
As @spatel notes in https://reviews.llvm.org/D49179#1158760,
that code is a rather complex mess, so we'll let it slide.

Reviewers: spatel, craig.topper

Reviewed By: spatel

Subscribers: yamauchi, majnemer, t.p.northover, llvm-commits

Differential Revision: https://reviews.llvm.org/D49179

llvm-svn: 336834
 2018-07-11 19:05:04 +00:00
Roman Lebedev 5260c9efc8 [NFC][InstCombine] Fix extra space padding in icmp-mul-zext.ll test 
update_test_checks will drop it anyway, creating noise..

llvm-svn: 336781
 2018-07-11 09:57:53 +00:00
Joseph Tremoulet 6f406d4f02 [InstCombine] Avoid iteration/mutation conflict 
Summary:
When iterating users of a multiply in processUMulZExtIdiom, the
call to setOperand in the truncation case may replace the use
being visited; make sure the iterator has been advanced before
doing that replacement.

Reviewers: majnemer, davide

Reviewed By: davide

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D48192

llvm-svn: 334844
 2018-06-15 16:52:40 +00:00
Sanjay Patel 49aafec2e6 [InstCombine] don't try to evaluate instructions with >1 use (revert r324014) 
This example causes a compile-time explosion:

define i16 @foo(i16 %in) {
  %x = zext i16 %in to i32
  %a1 = mul i32 %x, %x
  %a2 = mul i32 %a1, %a1
  %a3 = mul i32 %a2, %a2
  %a4 = mul i32 %a3, %a3
  %a5 = mul i32 %a4, %a4
  %a6 = mul i32 %a5, %a5
  %a7 = mul i32 %a6, %a6
  %a8 = mul i32 %a7, %a7
  %a9 = mul i32 %a8, %a8
  %a10 = mul i32 %a9, %a9
  %a11 = mul i32 %a10, %a10
  %a12 = mul i32 %a11, %a11
  %a13 = mul i32 %a12, %a12
  %a14 = mul i32 %a13, %a13
  %a15 = mul i32 %a14, %a14
  %a16 = mul i32 %a15, %a15
  %a17 = mul i32 %a16, %a16
  %a18 = mul i32 %a17, %a17
  %a19 = mul i32 %a18, %a18
  %a20 = mul i32 %a19, %a19
  %a21 = mul i32 %a20, %a20
  %a22 = mul i32 %a21, %a21
  %a23 = mul i32 %a22, %a22
  %a24 = mul i32 %a23, %a23
  %T = trunc i32 %a24 to i16
  ret i16 %T
}

 

llvm-svn: 324276
 2018-02-05 21:50:32 +00:00
Sanjay Patel 3343fcef86 [InstCombine] allow multi-use values in canEvaluate* if all uses are in 1 inst 
This is the enhancement suggested in D42536 to fix a shortcoming in 
regular InstCombine's canEvaluate* functionality.
When we have multiple uses of a value, but they're all in one instruction, we can 
allow that expression to be narrowed or widened for the same cost as a single-use 
value.

AFAICT, this can only matter for multiply: sub/and/or/xor/select would be simplified 
away if the operands are the same value; add becomes shl; shifts with a variable shift 
amount aren't handled.

Differential Revision: https://reviews.llvm.org/D42739

llvm-svn: 324014
 2018-02-01 21:55:53 +00:00
Sanjay Patel fd58ade81c [InstCombine] move related tests into the same file; NFC 
llvm-svn: 323882
 2018-01-31 15:47:59 +00:00