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Teaching SimplifyCFG to recognize the Or-Mask trick that InstCombine uses to

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reduce the number of comparisons.

Specifically, InstCombine can turn:
  (i == 5334 || i == 5335)
into:
  ((i | 1) == 5335)

SimplifyCFG was already able to detect the pattern:
  (i == 5334 || i == 5335)
to:
  ((i & -2) == 5334)

This patch supersedes D21315 and resolves PR27555
(https://llvm.org/bugs/show_bug.cgi?id=27555).

Thanks to David and Chandler for the suggestions!

Author: Thomas Jablin (tjablin)
Reviewers: majnemer chandlerc halfdan cycheng

http://reviews.llvm.org/D21397

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@273639 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chuang-Yu Cheng 2016-06-24 01:59:00 +00:00
parent 1d084dfa7b
commit fa7c6a0a04
2 changed files with 64 additions and 0 deletions
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25
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -461,6 +461,9 @@ private:
QUERY( (y & ~mask = y) =>
((x & ~mask = y) <=> (x = y OR x = (y | mask)))
);
QUERY( (y | mask = y) =>
((x | mask = y) <=> (x = y OR x = (y & ~mask)))
);
*/
// Please note that each pattern must be a dual implication (<--> or
@ -503,6 +506,28 @@ private:
}
}
// Pattern match a special case:
/*
QUERY( (y | mask = y) =>
((x | mask = y) <=> (x = y OR x = (y & ~mask)))
);
*/
if (match(ICI->getOperand(0),
m_Or(m_Value(RHSVal), m_APInt(RHSC)))) {
APInt Mask = *RHSC;
if (Mask.isPowerOf2() && (C->getValue() | Mask) == C->getValue()) {
// If we already have a value for the switch, it has to match!
if (!setValueOnce(RHSVal))
return false;
Vals.push_back(C);
Vals.push_back(ConstantInt::get(C->getContext(),
C->getValue() & ~Mask));
UsedICmps++;
return true;
}
}
// If we already have a value for the switch, it has to match!
if (!setValueOnce(ICI->getOperand(0)))
return false;

39
test/Transforms/SimplifyCFG/switch_create.ll
View File

@ -616,6 +616,45 @@ if:
call void @foo1()
ret void
else:
ret void
}
; Form a switch when or'ing a power of two
; CHECK-LABEL: define void @test21
; CHECK: i32 32, label %else
; CHECK: i32 13, label %else
; CHECK: i32 12, label %else
define void @test21(i32 %arg) {
%and = or i32 %arg, 1
%cmp1 = icmp ne i32 %and, 13
%cmp2 = icmp ne i32 %arg, 32
%pred = and i1 %cmp1, %cmp2
br i1 %pred, label %if, label %else
if:
call void @foo1()
ret void
else:
ret void
}
; Since %cmp1 is always false, a switch is never formed
; CHECK-LABEL: define void @test22
; CHECK-NOT: switch
; CHECK: ret void
define void @test22(i32 %arg) {
%and = or i32 %arg, 1
%cmp1 = icmp ne i32 %and, 12
%cmp2 = icmp ne i32 %arg, 32
%pred = and i1 %cmp1, %cmp2
br i1 %pred, label %if, label %else
if:
call void @foo1()
ret void
else:
ret void
}