[PATCH] D68360: PR41162 Implement LKK remainder and divisibility algorithms [urem]
Roman Lebedev via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Oct 7 15:11:31 PDT 2019
lebedev.ri added a comment.
It looks that we now use hacker's deligth lowering for urem?
Where is that lowering being performed?
================
Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:4934
+ const APInt &D = DivisorConstant->getAPIntValue();
+ APInt C = APInt::getMaxValue(F).udiv(D.zext(F)).uadd_sat(APInt(F, 1));
+ SDValue AproximateReciprocal = DAG.getConstant(C, DL, FVT.getScalarType());
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This should be a simple `add`.
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Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:4941-4943
+ if (!D.isStrictlyPositive() || D.isMaxValue() || D.isOneValue() ||
+ D.isPowerOf2()) {
+ // Divisor must be in the range of (1,2^N)
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There is no such restriction.
================
Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:4944-4945
+ // Divisor must be in the range of (1,2^N)
+ // We can lower remainder of division by powers of two much better
+ // elsewhere.
+ return false;
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I believe what you want to do, is to check whether *all* divisors are powers of two, and avoid *this* fold then.
If at least one of them is not a power of two this should still be good.
That being said many of the test changes look like regressions.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D68360/new/
https://reviews.llvm.org/D68360
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