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Author SHA1 Message Date
Nikita Popov 221f3fc750 [InstSimplify] Simplify saturating add/sub + icmp 
If a saturating add/sub has one constant operand, then we can
determine the possible range of outputs it can produce, and simplify
an icmp comparison based on that.

The implementation is based on a similar existing mechanism for
simplifying binary operator + icmps.

Differential Revision: https://reviews.llvm.org/D55735

llvm-svn: 349369
 2018-12-17 17:45:18 +00:00
Nikita Popov 32083bd072 [InstCombine] Add additional saturating add/sub + icmp tests; NFC 
These test comparisons with saturating add/sub in non-canonical
form.

llvm-svn: 349309
 2018-12-16 17:45:25 +00:00
Nikita Popov f61567f42a [InstSimplify] Add tests for saturating add/sub + icmp; NFC 
If a saturating add/sub with a constant operand is compared to
another constant, we should be able to determine that the condition
is always true/false in some cases (but currently don't).

llvm-svn: 349261
 2018-12-15 10:37:01 +00:00
Sanjay Patel eea21da12a [InstructionSimplify] Add support for saturating add/sub 
Add support for saturating add/sub in InstructionSimplify. In particular, the following simplifications are supported:

    sat(X + 0) -> X
    sat(X + undef) -> -1
    sat(X uadd MAX) -> MAX
    (and commutative variants)

    sat(X - 0) -> X
    sat(X - X) -> 0
    sat(X - undef) -> 0
    sat(undef - X) -> 0
    sat(0 usub X) -> 0
    sat(X usub MAX) -> 0

Patch by: @nikic (Nikita Popov)

Differential Revision: https://reviews.llvm.org/D54532

llvm-svn: 347330
 2018-11-20 17:20:26 +00:00
Sanjay Patel f967328e24 [InstSimplify] add tests for saturating add/sub; NFC 
These are baseline tests for D54532.
Patch based on the original tests by:
@nikic (Nikita Popov)

llvm-svn: 347060
 2018-11-16 16:32:34 +00:00