[clang] [llvm] [AMDGPU] Match bitsin(typeof(x)) - popcnt(x) to s_bcnt0_i32 (PR #164847)

[Patrick Simmons via cfe-commits]

================
@@ -0,0 +1,110 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
+; RUN: llc -mtriple=amdgcn -mcpu=gfx900 < %s | FileCheck %s
----------------
linuxrocks123 wrote:

@arsenm

```LLVM ERROR: unable to map instruction: %8:sreg_32 = COPY %7:vgpr(s32) (in function: bcnt032_not_for_vregs)```

It requires the test _WITHOUT_ your suggested changes to cause the crash.  I updated them per your comments, but please let me know if you'd like me to revert that commit to preserve the crashing testcase.  (I can add an XFAIL line.)

https://github.com/llvm/llvm-project/pull/164847