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Summary: When X = 0 and Y = inf, the original code produces inf, but the transformed code produces nan. So this transform (and its relatives) should only be used when the no-infs-fp-math flag is explicitly enabled. Also disable the transform using fmad (intermediate rounding) when unsafe-math is not enabled, since it can reduce the precision of the result; consider this example with binary floating point numbers with two bits of mantissa: x = 1.01 y = 111 x * (y + 1) = 1.01 * 1000 = 1010 (this is the exact result; no rounding occurs at any step) x * y + x = 1000.11 + 1.01 =r 1000 + 1.01 = 1001.01 =r 1000 (with rounding towards zero) The example relies on rounding towards zero at least in the second step. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98578 Reviewers: RKSimon, tstellarAMD, spatel, arsenm Subscribers: wdng, llvm-commits Differential Revision: https://reviews.llvm.org/D26602 llvm-svn: 288506
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