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It is possible for several constants which aren't individually absorbing to
combine to the absorbing element. Thanks to nbjoerg on IRC for pointing this out. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158399 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -629,8 +629,13 @@ static bool LinearizeExprTree(BinaryOperator *I,
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// Add any constants back into Ops, all globbed together and reduced to having
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// weight 1 for the convenience of users.
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Constant *Identity = ConstantExpr::getBinOpIdentity(Opcode, I->getType());
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if (Cst && Cst != Identity)
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if (Cst && Cst != Identity) {
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// If combining multiple constants resulted in the absorber then the entire
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// expression must evaluate to the absorber.
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if (Cst == Absorber)
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Ops.clear();
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Ops.push_back(std::make_pair(Cst, APInt(Bitwidth, 1)));
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}
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// For nilpotent operations or addition there may be no operands, for example
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// because the expression was "X xor X" or consisted of 2^Bitwidth additions:
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11
test/Transforms/Reassociate/absorption.ll
Normal file
11
test/Transforms/Reassociate/absorption.ll
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@ -0,0 +1,11 @@
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; RUN: opt -S -reassociate < %s | FileCheck %s
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; Check that if constants combine to an absorbing value then the expression is
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; evaluated as the absorbing value.
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define i8 @foo(i8 %x) {
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%tmp1 = or i8 %x, 127
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%tmp2 = or i8 %tmp1, 128
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ret i8 %tmp2
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; CHECK: @foo
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; CHECK: ret i8 -1
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}
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