[PATCH] D74484: [AggressiveInstCombine] Add support for ICmp instr that feeds a select intsr's condition operand.

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

This seems not generic enough to me, can't we not require the icmp operands to be constants/[sz]ext's,
but instead try to see if it can be evaluated in smaller bitwidth (what the rest of the code here does)?

As long as the icmp can be shrunked to at least as small bitwidth as we need there to get rid of cast,
i think we can always pick the actual bitwidth we'll use, which might be wider than minimal?



================
Comment at: llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp:171
+// Get the minimum number of bits needed for the given constant.
+static unsigned getConstMinBitWidth(bool IsSigned, ConstantInt *C) {
+  // If the const value is signed and negative, count the leading ones.
----------------
You want to operate on `APInt`, not assuming that it fits into 64-bits.
This is a correctness issue.


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  https://reviews.llvm.org/D74484/new/

https://reviews.llvm.org/D74484