Disable Altivec instructions on PowerPC unless requested #337
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Baseline PowerPC CPUs are not guaranteed to have Altivec instructions available, even if they are 64-bit. Unlike SSE and similar extensions on x86, there does not seem to be a way to enable conditional, targeted use of Altivec based on runtime detection (which is what ioquake3 wants to do) without also giving the compiler permission to use Altivec in code generation; so to not crash on the affected CPUs, we'll have to turn it off altogether. At one point Altivec was an important optimization, because the most commonly available PowerPC CPUs (in Apple G4/G5 hardware) had the Altivec instructions, and they were a significant benefit there. However, Apple haven't sold PowerPC devices for over 10 years, some more recently-manufactured PowerPC CPUs like the (64-bit) Freescale e5500 omit Altivec, and CPUs in general are a lot faster now than they were when the idTech3 engine was first released, hopefully making the optimization unnecessary. This commit uses -mno-altivec to force Altivec instructions not to be emitted, unless Altivec is requested via "make USE_ALTIVEC=1". The Apple fork of gcc doesn't document the corresponding -fno-altivec option, so we'll have to assume that omitting -faltivec is enough (but non-Altivec Macs haven't been sold for a long time anyway). Bug: ioquake#181 Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=701561 Tested-by: casey-ac <https://github.com/casey-ac>
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#368 is an alternative to this PR. |
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Fixed using a different method by #368. |
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Baseline PowerPC CPUs are not guaranteed to have Altivec instructions
available, even if they are 64-bit.
Unlike SSE and similar extensions on x86, there does not seem to be
a way to enable conditional, targeted use of Altivec based on runtime
detection (which is what ioquake3 wants to do) without also giving the
compiler permission to use Altivec in code generation; so to not crash
on the affected CPUs, we'll have to turn it off altogether.
At one point Altivec was an important optimization, because the
most commonly available PowerPC CPUs (in Apple G4/G5 hardware)
had the Altivec instructions, and they were a significant benefit
there. However, Apple haven't sold PowerPC devices for over 10 years,
some more recently-manufactured PowerPC CPUs like the (64-bit) Freescale
e5500 omit Altivec, and CPUs in general are a lot faster now than they
were when the idTech3 engine was first released, hopefully making the
optimization unnecessary.
This commit uses -mno-altivec to force Altivec instructions not to be
emitted, unless Altivec is requested via "make USE_ALTIVEC=1". The Apple
fork of gcc doesn't document the corresponding -fno-altivec option, so
we'll have to assume that omitting -faltivec is enough (but non-Altivec
Macs haven't been sold for a long time anyway).
Bug: #181
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=701561
Tested-by: @casey-ac