This patch replaces the IR based truncateToMinimalBitwidths with a VPlan
version. This has 3 benefits:
1) the VPlan-based version is simpler; we don't need to implement
special codegen for each supported instruction type like the IR based
one.
2) Removes a dependency on the cost-model after VPlan execution and
3) Removes a use of getVPValue that uses underlying values after VPlan
execution (See removed FIXME).
Depends on D149081.
Depends on D149079.
Reviewed By: Ayal
Differential Revision: https://reviews.llvm.org/D149903
Split off from D150398 to avoid builder-related diff changes there.
Using IRBuilder to create ICmps simplifies the result if both operands
are constants.
Reviewed By: Ayal
Differential Revision: https://reviews.llvm.org/D158332
Update computeMinimumValueSizes to check if an instruction's operands
can safely be truncated.
If more than MinBW bits are demanded by for the operand or if the
operand is a constant and cannot be safely truncated, it is not safe to
evaluate the instruction in the narrower MinBW. Skip those cases.
Fixes https://github.com/llvm/llvm-project/issues/47927
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D154717
