https://llvm.org/bugs/show_bug.cgi?id=23418
Bug ID: 23418
Summary: Support TEST DATA CLASS instruction
Product: libraries
Version: trunk
Hardware: Other
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: SystemZ
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
System z provides a TEST DATA CLASS instruction that could be used to
implement any of the floating-point test builtins, including isfinite,
isinf, isnan, or isnormal.
To implement that, the back-end should recognize the typical idioms
used to implement those checks and convert them into TDC primitives,
and then collect multiple such primitives when possible.
For example, __builtin_isfinite (f) is represented in LLVM IR as:
%iseq = fcmp ord double %f, 0.000000e+00
%0 = tail call double @llvm.fabs.f64(double %f)
%isinf = fcmp une double %0, 0x7FF0000000000000
%and = and i1 %iseq, %isinf
Via repeated application of the following rules:
%y = fcmp ord double %x, 0.000000e+00
--> %y = TDC %x, 0xff0
%y = fcmp une double %x, 0x7FF0000000000000
--> %y = TDC %x, 0xfdf
%y = tail call double @llvm.fabs.f64(double %x)
%z = TDC %y, %mask
--> %z = TDC %x, (%mask & 0xaaa) | ((%mask & 0xaaa) >> 1)
%y = TDC %x, %mask1
%z = TDC %x, %mask2
%t = and i1 %y %z
--> %t = TDC %x, %mask1 & %mask2
this could be simplified to:
%and = TDC %f, 0xfc0
which implements exactly the "isfinite" logic.
(The above is just a subset of rules that could be applicable for a fully
generic implementation.)
It should be possible to do this during SelectionDAG isel.
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