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Author SHA1 Message Date
Sanjay Patel 0d4fd5b668 [InstSimplify] fold sdiv/srem based on compare of dividend and divisor 
This should bring signed div/rem analysis up to the same level as unsigned. 
We use icmp simplification to determine when the divisor is known greater than the dividend.

Each positive test is followed by a negative test to show that we're not overstepping the boundaries of the known bits.
There are extra tests for the signed-min-value special cases.

Alive proofs:
http://rise4fun.com/Alive/WI5

Differential Revision: https://reviews.llvm.org/D37713

llvm-svn: 313264
 2017-09-14 14:59:07 +00:00
Sanjay Patel bb1b1c97fa [InstSimplify] fix some test names; NFC 
Too much division...the quotient is the answer.

llvm-svn: 312943
 2017-09-11 20:38:31 +00:00
Sanjay Patel a36eb77118 [InstSimplify] add tests for possible sdiv/srem simplifications; NFC 
As noted in PR34517, the handling of signed div/rem is not on par with
unsigned div/rem. Signed is harder to reason about, but it should be
possible to handle at least some of these using the same technique that
we use for unsigned: use icmp logic to see if there's a relationship
between the quotient and divisor.

llvm-svn: 312938
 2017-09-11 19:42:41 +00:00