[NVPTX] Implement NVPTXTargetLowering::getSqrtEstimate.
Summary:
This lets us lower to sqrt.approx and rsqrt.approx under more
circumstances.
* Now we emit sqrt.approx and rsqrt.approx for calls to @llvm.sqrt.f32,
when fast-math is enabled. Previously, we only would emit it for
calls to @llvm.nvvm.sqrt.f. (With this patch we no longer emit
sqrt.approx for calls to @llvm.nvvm.sqrt.f; we rely on intcombine to
simplify llvm.nvvm.sqrt.f into llvm.sqrt.f32.)
* Now we emit the ftz version of rsqrt.approx when ftz is enabled.
Previously, we only emitted rsqrt.approx when ftz was disabled.
Reviewers: hfinkel
Subscribers: llvm-commits, tra, jholewinski
Differential Revision: https://reviews.llvm.org/D28508
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293605
91177308-0d34-0410-b5e6-
96231b3b80d8
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