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
diff --git a/lib/Support/APFloat.cpp b/lib/Support/APFloat.cpp
index abe5575..3a63258 100644
--- a/lib/Support/APFloat.cpp
+++ b/lib/Support/APFloat.cpp
@@ -3583,6 +3583,14 @@
if (reciprocal.divide(*this, rmNearestTiesToEven) != opOK)
return false;
+ // Avoid multiplication with a denormal, it is not safe on all platforms and
+ // may be slower than a normal division.
+ if (reciprocal.significandMSB() + 1 < reciprocal.semantics->precision)
+ return false;
+
+ assert(reciprocal.category == fcNormal &&
+ reciprocal.significandLSB() == reciprocal.semantics->precision - 1);
+
if (inv)
*inv = reciprocal;