[PATCH] D86547: [compiler-rt][builtins] Use c[tl]zsi macro instead of __builtin_c[tl]z

[Anatoly Trosinenko via Phabricator via cfe-commits]

atrosinenko added a comment.

In D86547#2284095 <https://reviews.llvm.org/D86547#2284095>, @MaskRay wrote:

> The `(aWidth - 1) - clzsi(a)` change is correct, but why is the ctz change?

`d.s.low` and `d.s.high` are `su_int`. While some helpers from `libgcc` are documented with `int`, `long`, etc. types //for simplicity// and use machine modes under the hood, the `__builtin_ctz()` function (as well as clz), on the other hand, seems to **really** accept an `int`-sized argument:

  $ clang --version
  clang version 10.0.0-4ubuntu1 
  Target: x86_64-pc-linux-gnu
  Thread model: posix
  InstalledDir: /usr/bin
  $ clang -S -O3 -o- -x c - <<< "int f() { return __builtin_ctz(0x100000); }"
          .text
          .file   "-"
          .globl  f                       # -- Begin function f
          .p2align        4, 0x90
          .type   f, at function
  f:                                      # @f
          .cfi_startproc
  # %bb.0:
          movl    $20, %eax
          retq
  .Lfunc_end0:
          .size   f, .Lfunc_end0-f
          .cfi_endproc
                                          # -- End function
          .ident  "clang version 10.0.0-4ubuntu1 "
          .section        ".note.GNU-stack","", at progbits
          .addrsig
  $ clang -S -O3 -target msp430 -o- -x c - <<< "int f() { return __builtin_ctz(0x100000); }"
  <stdin>:1:32: warning: implicit conversion from 'long' to 'unsigned int' changes value from 1048576 to 0 [-Wconstant-conversion]
  int f() { return __builtin_ctz(0x100000); }
                   ~~~~~~~~~~~~~ ^~~~~~~~
          .text
          .file   "-"
          .globl  f                       ; -- Begin function f
          .p2align        1
          .type   f, at function
  f:                                      ; @f
  ; %bb.0:
          ret
  .Lfunc_end0:
          .size   f, .Lfunc_end0-f
                                          ; -- End function
          .ident  "clang version 10.0.0-4ubuntu1 "
          .section        ".note.GNU-stack","", at progbits
          .addrsig
  1 warning generated.


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