[llvm-bugs] [Bug 39865] New: [PowerPC] Support half/f16

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Mon Dec 3 06:33:18 PST 2018


            Bug ID: 39865
           Summary: [PowerPC] Support half/f16
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: v.churavy at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

I was exploring adding support for half/f16 in the Julia frontend and while
testing on PPC I discovered that the backend doesn't support instructions
targeting f16.

I am in particular interested in f16 support since the codegen of the Julia
front-end does not differentiate between GPU/CPU codegen and I want to target
NVIDIAs native f16 support. It would be absolutely fine if the PPC backend
bails out early and emits library-calls.

I no longer have my particular test-case at hand, but running the fairly
generic X86 testcase yields:

➜  llvm git:(master) llc  -mtriple=ppc64le-unknown-linux-gnu

LLVM ERROR: Cannot select: 0x561ac6ea0158: f32,ch = load<(load 2 from
%ir.addr), anyext from f16> 0x561ac6e408f8, 0x561ac6e9ffb8, undef:i64
  0x561ac6e9ffb8: i64,ch = CopyFromReg 0x561ac6e408f8, Register:i64 %0
    0x561ac6ea0290: i64 = Register %0
  0x561ac6ea0088: i64 = undef
In function: test_extend32

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