aarch64: fix reg/imm sub insts that read SP, not the zero register.
#2548
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On AArch64, the zero register (xzr) and the stack pointer (xsp) are alternately named by the same index `31` in machine code depending on context. In particular, in the reg-reg-immediate ALU instruction form, add/subtract will use the stack pointer, not the zero register, if index 31 is given for the first (register) source arg. In a few places, we were emitting subtract instructions with the zero register as an argument and a reg/immediate as the second argument. When an immediate could be incorporated directly (we have the `iconst` definition visible), this would result in incorrect code being generated. This issue was found in `ineg` and in the sequence for vector right-shifts. Reported by Ian Cullinan; thanks!
julian-seward1
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Jan 14, 2021
On AArch64, the zero register (xzr) and the stack pointer (xsp) are alternately named by the same index `31` in machine code depending on context. In particular, in the reg-reg-immediate ALU instruction form, add/subtract will use the stack pointer, not the zero register, if index 31 is given for the first (register) source arg. In a few places, we were emitting subtract instructions with the zero register as an argument and a reg/immediate as the second argument. When an immediate could be incorporated directly (we have the `iconst` definition visible), this would result in incorrect code being generated. This issue was found in `ineg` and in the sequence for vector right-shifts. Reported by Ian Cullinan; thanks! (cherry picked from commit aac3751) (this is bytecodealliance#2548)
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On AArch64, the zero register (xzr) and the stack pointer (xsp) are
alternately named by the same index
31in machine code depending oncontext. In particular, in the reg-reg-immediate ALU instruction form,
add/subtract will use the stack pointer, not the zero register, if index
31 is given for the first (register) source arg.
In a few places, we were emitting subtract instructions with the zero
register as an argument and a reg/immediate as the second argument. When
an immediate could be incorporated directly (we have the
iconstdefinition visible), this would result in incorrect code being
generated.
This issue was found in
inegand in the sequence for vectorright-shifts.
Reported by Ian Cullinan; thanks!