[all-commits] [llvm/llvm-project] 1e5ebb: [InstCombine] Fold exp2(uitofp x) to ldexp(1.0, x)...

[Harrison Hao via All-commits]

  Branch: refs/heads/users/harrisonGPU/instcombine/exp2-to-ldexp
  Home:   https://github.com/llvm/llvm-project
  Commit: 1e5ebb6546e7a04133dcc07ab7d2541b2a7a550a
      https://github.com/llvm/llvm-project/commit/1e5ebb6546e7a04133dcc07ab7d2541b2a7a550a
  Author: Harrison Hao <tsworld1314 at gmail.com>
  Date:   2026-10-01 (Thu, 01 Oct 2026)

  Changed paths:
    M llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
    M llvm/test/Transforms/InstCombine/exp2-1.ll
    M llvm/test/Transforms/InstCombine/exp2-to-ldexp.ll
    M llvm/test/Transforms/InstCombine/pow-to-ldexp.ll
    M llvm/test/Transforms/InstCombine/pow_fp_int.ll
    M llvm/test/Transforms/InstCombine/pow_fp_int16.ll

  Log Message:
  -----------
  [InstCombine] Fold exp2(uitofp x) to ldexp(1.0, x) with ninf

`exp2(uitofp iN x) -> ldexp(1.0, zext x)` currently requires N to be
narrower than `int`, because `ldexp` takes a signed `int` exponent.
When N equals the width of `int`, the fold is still correct under `ninf`.
Every LLVM FP type has $E_{\max} \le 16383 < 2^{15} \le 2^{N-1}$, so:

- $x < 2^{N-1}$: signed and unsigned $x$ agree, so $\operatorname{ldexp}(1.0, x) = 2^{x} = \operatorname{exp2}(x)$.
- $x \ge 2^{N-1}$: $\operatorname{exp2}(x) \ge 2^{2^{N-1}} > 2^{E_{\max}}$ overflows to $+\infty$, which is poison under `ninf`.

This only applies to the intrinsic, since the `exp2` libcall may set
`errno` on overflow.

This also enables `pow(2.0, uitofp x) -> ldexp` via the existing
`pow(2^n, x) -> exp2(n * x)` fold.


  Commit: a68a8f9222cb235274fbcb69364326d522fe6acc
      https://github.com/llvm/llvm-project/commit/a68a8f9222cb235274fbcb69364326d522fe6acc
  Author: Harrison Hao <tsworld1314 at gmail.com>
  Date:   2026-10-01 (Thu, 01 Oct 2026)

  Changed paths:
    M llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
    M llvm/test/Transforms/InstCombine/exp2-1.ll
    M llvm/test/Transforms/InstCombine/exp2-to-ldexp.ll

  Log Message:
  -----------
  Update for comments


Compare: https://github.com/llvm/llvm-project/compare/3cc13c858ff0...a68a8f9222cb

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