[BUG] Function multiversioning FEAT conditions are incorrect #320
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I'd like to run the same function on both SVE core and SVE2 core using FMV. But FMV doesn't work as expected because of this odd definition. So I posted this issue to LLVM. Could you fix it ? |
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It seems to me this is not specific to SVE, more features may be affected. We should be checking >= rather than equality. |
labrinea
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Some features are later versions of others, like sve2 and sve, therefore performing equality checks on system register values would incur incorrect feature detection on later hardware. See ARM-software#320 for example. Therefore we should instead do >= comparisons when HWCAP info is not available. I am also fixing incorrect detection for LSE and WFxT.
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labrinea
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Some features are later versions of others, like sve2 and sve, therefore performing equality checks on system register values would incur incorrect feature detection on later hardware. See ARM-software#320 for example. Therefore we should instead do >= comparisons when HWCAP info is not available. I am also fixing incorrect detection for LSE and WFxT. Lastly to detect SVE2 and SME2 I am using the SVEVer and SMEVer bitfields respectively.
labrinea
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Some features are later versions of others, like sve2 and sve, therefore performing equality checks on system register values would incur incorrect feature detection on later hardware. See ARM-software#320 for example. Therefore we should instead do >= comparisons when HWCAP info is not available. I am also fixing incorrect detection for LSE and WFxT. Lastly to detect SVE2 and SME2 I am using the SVEVer and SMEVer bitfields respectively.
labrinea
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Some features are later versions of others, like sve2 and sve, therefore performing equality checks on system register values would incur incorrect feature detection on later hardware. See ARM-software#320 for example. Therefore we should instead do >= comparisons when HWCAP info is not available. I am also fixing incorrect detection for LSE and WFxT. Lastly to detect SVE2 and SME2 I am using the SVEVer and SMEVer bitfields respectively.
labrinea
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Some features are later versions of others, like sve2 and sve, therefore performing equality checks on system register values would incur incorrect feature detection on later hardware. See ARM-software#320 for example. Therefore we should instead do >= comparisons when HWCAP info is not available. I am also fixing incorrect detection for LSE and WFxT. Lastly to detect SVE2 and SME2 I am using the SVEVer and SMEVer bitfields respectively.
vhscampos
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Some features are later versions of others, like sve2 and sve, therefore performing equality checks on system register values would incur incorrect feature detection on later hardware. See #320 for example. Therefore we should instead do >= comparisons when HWCAP info is not available. I am also fixing incorrect detection for LSE and WFxT. Lastly to detect SVE2 and SME2 I am using the SVEVer and SMEVer bitfields respectively.
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In acle.md the table describing multiversioning has many entries like this:
310 FEAT_SVE sve ID_AA64PFR0_EL1.SVE != 0b0000 AND ID_AA64ZFR0_EL1.SVEver == 0b0000In almost all cases using equality comparison is incorrect. The above means a multiversioned function for SVE would never be selected on a core with SVE2. So these version checks need to use
>=, never==.Also, why not list the HWCAP instead as that is what actual implementations will use?
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