[llvm] [X86][NFC] Moved/Updated FNEG testcases (PR #162269)

[Evgenii Kudriashov via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
+; RUN: llc < %s -mtriple=i686-linux-gnu -fast-isel                            | FileCheck %s --check-prefixes=X86,FASTISEL-X86
+; RUN: llc < %s -mtriple=i686-linux-gnu -global-isel=0 -fast-isel=0           | FileCheck %s --check-prefixes=X86,SDAG-X86
+; DISABLED: llc < %s -mtriple=i686-linux-gnu -global-isel=1 -global-isel-abort=2   | FileCheck %s --check-prefixes=X86,GISEL-X86
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e-kud wrote:

If an opcode is not mentioned in the legalizer, GlobalISel tries to `lower()` by default. We end up with the situation when floats and doubles are handled on GPRs but the result need to be returned using X87 stack, so we get `fp0 = COPY eax`. IIRC FPStackifier is not happy with it. Once we legalize using X87 stack, we don have this problem. So it is a mix of the default lowering and GlobalISel generating such copies between register classes.

https://github.com/llvm/llvm-project/pull/162269