tree a282fbb98a41d5f582eb64e4db7ba47e2a10e433
parent 9a16248dedf36fe2ff515a2e6def852ade6784ed
author Nicolas Capens <capn@google.com> 1550259663 -0500
committer Nicolas Capens <nicolascapens@google.com> 1551195685 +0000

Work around x86-64 calling convention bug

Microsoft's x86-64 calling convention ABI requires registers XMM6-15 to
be preserved by the callee:
https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention?view=vs-2017#calling-convention-defaults
Currently only the System V calling convention's behavior is supported,
which does not have any callee-saved XMM registers.

Fixing this properly is non-trivial and this bug is blocking other
projects, so a temporary workaround is to limit Subzero to use only
scratch registers XMM0-XMM5.

Bug chromium:931926
Bug swiftshader:22

Change-Id: If3fde2295fc65fc52042124afe7dfc46873cce3f
Reviewed-on: https://swiftshader-review.googlesource.com/c/25568
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>