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Avoid turning a floating point division with a constant power of two into a denormal multiplication.
Some platforms may treat denormals as zero, on other platforms multiplication with a subnormal is slower than dividing by a normal. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128555 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -3583,6 +3583,14 @@ bool APFloat::getExactInverse(APFloat *inv) const {
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if (reciprocal.divide(*this, rmNearestTiesToEven) != opOK)
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return false;
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// Avoid multiplication with a denormal, it is not safe on all platforms and
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// may be slower than a normal division.
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if (reciprocal.significandMSB() + 1 < reciprocal.semantics->precision)
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return false;
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assert(reciprocal.category == fcNormal &&
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reciprocal.significandLSB() == reciprocal.semantics->precision - 1);
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if (inv)
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*inv = reciprocal;
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@ -13,7 +13,7 @@ define float @test2(float %x) nounwind readnone ssp {
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ret float %div
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; CHECK: @test2
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; CHECK-NEXT: fmul float %x, 0x3800000000000000
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; CHECK-NEXT: fdiv float %x, 0x47E0000000000000
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}
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define float @test3(float %x) nounwind readnone ssp {
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@ -589,10 +589,8 @@ TEST(APFloatTest, exactInverse) {
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EXPECT_TRUE(APFloat(1.17549435e-38f).getExactInverse(&inv));
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EXPECT_TRUE(inv.bitwiseIsEqual(APFloat(8.5070592e+37f)));
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// Large float
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EXPECT_TRUE(APFloat(1.7014118e38f).getExactInverse(&inv));
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EXPECT_TRUE(inv.bitwiseIsEqual(APFloat(5.8774718e-39f)));
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// Large float, inverse is a denormal.
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EXPECT_FALSE(APFloat(1.7014118e38f).getExactInverse(0));
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// Zero
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EXPECT_FALSE(APFloat(0.0).getExactInverse(0));
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// Denormalized float
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