Checked on hardware that this bias was not added because I had assumed the other way around would be true, forgot to ask about making a PR for this when I initially had done so
If we're on an x64 CPU that doesn't have the MOVBE extension, trying to
SwapAndStore a host register results in that register's value getting
clobbered with the swapped value. Jit64::stX and Jit64::stXx detect this
case, and if necessary, emit a MOV to a register that's fine to clobber.
This logic was broken by the merge of PR 12134. Jit64::stX and
Jit64::stXx were assuming that if RegCache::IsImm returns true for a
guest register, calling RegCache::Use or RegCache::BindOrImm for that
guest register would result in an immediate. However, PR 12134 made it
possible for a guest register to have both a host register and an
immediate in the register cache at the same time. When this happens,
RegCache::IsImm returns true, yet RegCache::Use and RegCache::BindForImm
return an RCOpArg whose Location returns a host register. (To make it
extra confusing, RCOpArg::IsImm calls RegCache::IsImm if the RCOpArg
came from RegCache, so RCOpArg::IsImm returns true!)
To fix this, in cases where Jit64::stX and Jit64::stXx explicitly need
an immediate to avoid having to emit an extra MOV, let's call
RegCache::Imm32 so that we're certain that we're getting an immediate.
This fixes an issue on older x64 CPUs that manifested as e.g. completely
broken graphics in Spyro: Enter the Dragonfly.
The constant propagation PR made it so that a guest register can be
present in the register cache as both a host register and an immediate
at the same time. If such a guest register is requested from the
register cache, the register cache prefers returning it as a host
register. However, RCOpArg::IsImm still returns true in this case. This
is confusing, especially since OpArg::IsImm does not return true if the
RCOpArg is converted into an OpArg.
This commit makes RCOpArg::IsImm check whether RCOpArg::Location returns
an immediate, so that RCOpArg::IsImm returns false when a host register
is being used. Code that wants to know whether an immediate exists in
the register cache rather than whether an immediate is currently being
used should call RegCache::IsImm instead.
JMC47andGitHub
Admiral H. CurtissandGitHub
Sintendo
Craig Carnell
Tillmann Karras
Joshua Vandaële
cristian64
Nuh Uh
Jordan Woyak
JosJuice