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Add CallSiteSplitting pass

Description

Add CallSiteSplitting pass

Summary:
This change add a pass which tries to split a call-site to pass
more constrained arguments if its argument is predicated in the control flow
so that we can expose better context to the later passes (e.g, inliner, jump
threading, or IPA-CP based function cloning, etc.).
As of now we support two cases :

  1. If a call site is dominated by an OR condition and if any of its arguments

are predicated on this OR condition, try to split the condition with more
constrained arguments. For example, in the code below, we try to split the
call site since we can predicate the argument (ptr) based on the OR condition.

Split from :

if (!ptr || c)
  callee(ptr);

to :

if (!ptr)
  callee(null ptr)  // set the known constant value
else if (c)
  callee(nonnull ptr)  // set non-null attribute in the argument
  1. We can also split a call-site based on constant incoming values of a PHI

For example,
from :

BB0:
 %c = icmp eq i32 %i1, %i2
 br i1 %c, label %BB2, label %BB1
BB1:
 br label %BB2
BB2:
 %p = phi i32 [ 0, %BB0 ], [ 1, %BB1 ]
 call void @bar(i32 %p)

to

BB0:
 %c = icmp eq i32 %i1, %i2
 br i1 %c, label %BB2-split0, label %BB1
BB1:
 br label %BB2-split1
BB2-split0:
 call void @bar(i32 0)
 br label %BB2
BB2-split1:
 call void @bar(i32 1)
 br label %BB2
BB2:
 %p = phi i32 [ 0, %BB2-split0 ], [ 1, %BB2-split1 ]

Reviewers: davidxl, huntergr, chandlerc, mcrosier, eraman, davide

Reviewed By: davidxl

Subscribers: sdesmalen, ashutosh.nema, fhahn, mssimpso, aemerson, mgorny, mehdi_amini, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D39137

Details

Committed
junbumlNov 3 2017, 12:01 PM
Reviewer
davidxl
Differential Revision
D39137: Add CallSiteSplitting pass
Parents
rL317350: [llvm-objcopy] Add support for dwarf fission
Branches
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