On 09/12/2013 11:03 PM, Hal Finkel wrote:
Hello,
Please review the attached patch which restores the libm sqrt* -> @llvm.sqrt*
mapping, but only in fast-math mode (specifically, when the UnsafeFPMath or
NoNaNsFPMath CodeGen options are enabled). The @llvm.sqrt* intrinsics have
slightly different semantics from the libm call, specifically, they are undefined
when given a non-zero negative number (the libm calls will always return NaN for
any negative number).
This mapping was removed in r100613, and replaced with a TODO, but at that time
the fast-math flags were not yet implemented. Now that we have these, restoring
this mapping is important because it will enable autovectorization of sqrt
calls in loops (at least in fast-math mode).
Patch?
Tobias
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