Thorsten Schütt 45162635bf
[GlobalISel] Combine [s,z]ext of undef into 0 (#117439)
Alternative for https://github.com/llvm/llvm-project/pull/113764

It builds on a minimalistic approach with the legality check in match
and a blind apply. The precise patterns are used for better compile-time
and modularity. It also moves the pattern check into combiner. While
unary_undef_to_zero and propagate_undef_any_op rely on custom C++ code
for pattern matching.

Is there a limit on the number of patterns?

G_ANYEXT of undef -> undef
G_SEXT of undef -> 0
G_ZEXT of undef -> 0

The combine is not a member of the post legalizer combiner for AArch64.

Test:
llvm/test/CodeGen/AArch64/GlobalISel/combine-cast.mir
2024-12-03 07:14:49 +01:00
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