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Fix a XOR reassociation bug.

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When Reassociator optimize "(x | C1)" ^ "(X & C2)", it may swap the two
subexpressions, however, it forgot to swap cached constants (of C1 and C2)
accordingly.

rdar://13739160


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180676 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Shuxin Yang 2013-04-27 18:02:12 +00:00
parent 595dd5af14
commit 4d4c54d29f
2 changed files with 33 additions and 3 deletions
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9
lib/Transforms/Scalar/Reassociate.cpp
View File

@ -1195,9 +1195,6 @@ bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2,
if (X != Opnd2->getSymbolicPart())
return false;
const APInt &C1 = Opnd1->getConstPart();
const APInt &C2 = Opnd2->getConstPart();
// This many instruction become dead.(At least "Opnd1 ^ Opnd2" will die.)
int DeadInstNum = 1;
if (Opnd1->getValue()->hasOneUse())
@ -1215,6 +1212,8 @@ bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2,
if (Opnd2->isOrExpr())
std::swap(Opnd1, Opnd2);
const APInt &C1 = Opnd1->getConstPart();
const APInt &C2 = Opnd2->getConstPart();
APInt C3((~C1) ^ C2);
// Do not increase code size!
@ -1230,6 +1229,8 @@ bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2,
} else if (Opnd1->isOrExpr()) {
// Xor-Rule 3: (x | c1) ^ (x | c2) = (x & c3) ^ c3 where c3 = c1 ^ c2
//
const APInt &C1 = Opnd1->getConstPart();
const APInt &C2 = Opnd2->getConstPart();
APInt C3 = C1 ^ C2;
// Do not increase code size
@ -1244,6 +1245,8 @@ bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2,
} else {
// Xor-Rule 4: (x & c1) ^ (x & c2) = (x & (c1^c2))
//
const APInt &C1 = Opnd1->getConstPart();
const APInt &C2 = Opnd2->getConstPart();
APInt C3 = C1 ^ C2;
Res = createAndInstr(I, X, C3);
}

27
test/Transforms/Reassociate/xor_reassoc.ll
View File

@ -164,3 +164,30 @@ define void @xor_bug1() {
%3 = and i64 undef, %2
ret void
}
; The bug was that when the compiler optimize "(x | c1)" ^ "(x & c2)", it may
; swap the two xor-subexpressions if they are not in canoninical order; however,
; when optimizer swaps two sub-expressions, if forgot to swap the cached value
; of c1 and c2 accordingly, hence cause the problem.
;
define i32 @xor_bug2(i32, i32, i32, i32) {
%5 = mul i32 %0, 123
%6 = add i32 %2, 24
%7 = add i32 %1, 8
%8 = and i32 %1, 3456789
%9 = or i32 %8, 4567890
%10 = and i32 %1, 543210987
%11 = or i32 %1, 891034567
%12 = and i32 %2, 255
%13 = xor i32 %9, %10
%14 = xor i32 %11, %13
%15 = xor i32 %5, %14
%16 = and i32 %3, 255
%17 = xor i32 %16, 42
%18 = add i32 %6, %7
%19 = add i32 %18, %12
%20 = add i32 %19, %15
ret i32 %20
;CHECK: @xor_bug2
;CHECK: xor i32 %5, 891034567
}