Thorsten Schütt 2906fcadb8 [GlobalISel] Combine G_MERGE_VALUES of x and zero (#116283) ...

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.

2024-11-16 08:00:21 +01:00

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