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Optimize square root squared (PR21126).

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When unsafe-fp-math is enabled, we can turn sqrt(X) * sqrt(X) into X.

This can happen in the real world when calculating x ** 3/2. This occurs
in test-suite/SingleSource/Benchmarks/BenchmarkGame/n-body.c.

Differential Revision: http://reviews.llvm.org/D5584



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218906 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjay Patel
2014-10-02 21:10:54 +00:00
parent 130d072eb7
commit 0ff4eb684f
2 changed files with 34 additions and 0 deletions
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lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+5
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@@ -531,6 +531,11 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
}
}
// sqrt(X) * sqrt(X) -> X
if (AllowReassociate && (Op0 == Op1))
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op0))
if (II->getIntrinsicID() == Intrinsic::sqrt)
return ReplaceInstUsesWith(I, II->getOperand(0));
// Under unsafe algebra do:
// X * log2(0.5*Y) = X*log2(Y) - X