There are a number of backends (specifically AArch64, AMDGPU, Mips, and
RISCV) which contain a “TODO: make CombinerHelper methods const”
comment. This PR does just that and makes all of the CombinerHelper
methods const, removes the TODO comments and makes the associated
instances const. This change makes some sense because the CombinerHelper
class simply modifies the state of _other_ objects to which it holds
pointers or references.
Note that AMDGPU contains an identical comment for an instance of
AMDGPUCombinerHelper (a subclass of CombinerHelper). I deliberately
haven’t modified the methods of that class in order to limit the scope
of the change. I’m happy to do so either now or as a follow-up.
into zext x
LegalizerHelper has two padding strategies: undef or zero.
see LegalizerHelper:273
see LegalizerHelper:315
This PR is about zero sugar and Coke Zero.
; CHECK-NEXT: [[MV2:%[0-9]+]]:_(s64) = G_MERGE_VALUES %a(s32),
[[C]](s32)
Please continue padding merge values.
// %bits_8_15:(s8) = G_CONSTANT i8 0
// %0:(s16) = G_MERGE_VALUES %bits_0_7:(s8), %bits_8_15:(s8)
%bits_8_15 is defined by zero. For optimization, we pick zext.
// %0:_(s16) = G_ZEXT %bits_0_7:(s8)
The upper bits of %0 are zero and the lower bits come from %bits_0_7.
into anyext x
; CHECK-NEXT: [[MV1:%[0-9]+]]:_(s64) = G_MERGE_VALUES [[TRUNC]](s32),
[[DEF]](s32)
Please continue padding merge values.
// %bits_8_15:_(s8) = G_IMPLICIT_DEF
// %0:_(s16) = G_MERGE_VALUES %bits_0_7:(s8), %bits_8_15:(s8)
%bits_8_15 is defined by undef. Its value is undefined and we can pick
an arbitrary value. For optimization, we pick anyext, which plays well
with the undefinedness.
// %0:_(s16) = G_ANYEXT %bits_0_7:(s8)
The upper bits of %0 are undefined and the lower bits come from
%bits_0_7.
