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.
