# Benefit

This patch fixes:
1. After `platform select ios-simulator`, `platform process list` will
now print processes which are running in the iOS simulator. Previously,
no process will be listed.
2. After `platform select ios-simulator`, `platform attach --name
<name>` will succeed. Previously, it will error out saying no process is
found.


# Several bugs that is being fixed

1. During the process listing, add `aarch64` to the list of CPU types
for which iOS simulators are checked for.
2. Given a candidate process, when checking for simulators, the original
code will find the desired environment variable (`SIMULATOR_UDID`) and
set the OS to iOS, but then the immediate next environment variable will
set it back to macOS.
3. For processes running on simulator, set the triple's `Environment` to
`Simulator`, so that such processes can pass the filtering [in this
line](https://fburl.com/8nivnrjx). The original code leave it as the
default `UnknownEnvironment`.



# Manual test

**With this patch:**
```
royshi-mac-home ~/public_llvm/build % bin/lldb
(lldb) platform select ios-simulator

(lldb) platform process list
240 matching processes were found on "ios-simulator"

PID    PARENT USER       TRIPLE                         NAME
====== ====== ========== ============================== ============================
40511  28844  royshi     arm64-apple-ios-simulator      FocusPlayground // my toy iOS app running on simulator
... // omit
28844  1      royshi     arm64-apple-ios-simulator      launchd_sim

(lldb) process attach --name FocusPlayground
Process 40511 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGSTOP
    frame #0: 0x0000000104e3cb70 libsystem_kernel.dylib`mach_msg2_trap + 8
libsystem_kernel.dylib`mach_msg2_trap:
->  0x104e3cb70 <+8>: ret
... // omit
```

**Without this patch:**
```
$ bin/lldb
(lldb) platform select ios-simulator

(lldb) platform process list
error: no processes were found on the "ios-simulator" platform

(lldb) process attach --name FocusPlayground
error: attach failed: could not find a process named FocusPlayground
```


# Unittest

See PR.

The function already exposes a work list to avoid deep recursion, this
commit starts utilizing it in a helper that could also lead to a deep
recursion.

We have observed this crash on `clang/test/C/C99/n590.c` with our
internal builds that enable aggressive optimizations and hit the limit
earlier than default release builds of Clang.

See the added test for an example with a deeper recursion that used to
crash in upstream Clang before this change with the following stack
trace:

```
  #0 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /usr/local/google/home/ibiryukov/code/llvm-project/llvm/lib/Support/Unix/Signals.inc:804:13
  #1 llvm::sys::RunSignalHandlers() /usr/local/google/home/ibiryukov/code/llvm-project/llvm/lib/Support/Signals.cpp:106:18
  llvm#2 SignalHandler(int, siginfo_t*, void*) /usr/local/google/home/ibiryukov/code/llvm-project/llvm/lib/Support/Unix/Signals.inc:0:3
  llvm#3 (/lib/x86_64-linux-gnu/libc.so.6+0x3fdf0)
  llvm#4 AnalyzeImplicitConversions(clang::Sema&, clang::Expr*, clang::SourceLocation, bool) /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:12772:0
  llvm#5 CheckCommaOperand /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:0:3
  llvm#6 AnalyzeImplicitConversions /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:12644:7
  llvm#7 AnalyzeImplicitConversions(clang::Sema&, clang::Expr*, clang::SourceLocation, bool) /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:12776:5
  llvm#8 CheckCommaOperand /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:0:3
  llvm#9 AnalyzeImplicitConversions /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:12644:7
 llvm#10 AnalyzeImplicitConversions(clang::Sema&, clang::Expr*, clang::SourceLocation, bool) /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:12776:5
 llvm#11 CheckCommaOperand /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:0:3
 llvm#12 AnalyzeImplicitConversions /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:12644:7
 llvm#13 AnalyzeImplicitConversions(clang::Sema&, clang::Expr*, clang::SourceLocation, bool) /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:12776:5
 llvm#14 CheckCommaOperand /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:0:3
 llvm#15 AnalyzeImplicitConversions /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:12644:7
 llvm#16 AnalyzeImplicitConversions(clang::Sema&, clang::Expr*, clang::SourceLocation, bool) /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:12776:5
 llvm#17 CheckCommaOperand /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:0:3
 llvm#18 AnalyzeImplicitConversions /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:12644:7
 llvm#19 AnalyzeImplicitConversions(clang::Sema&, clang::Expr*, clang::SourceLocation, bool) /usr/local/google/home/ibiryukov/code/llvm-project/clang/lib/Sema/SemaChecking.cpp:12776:5
... 700+ more stack frames.
```

Fix unnecessary conversion of C-String to StringRef in the `Cmp` lambda
inside `lookupLLVMIntrinsicByName`. This both fixes an ASAN error in the
code that happens when the `Name` StringRef passed in is not a Null
terminated StringRef, and additionally can potentially speed up the code
as well by eliminating the unnecessary computation of string length
every time a C String is converted to StringRef in this code (It seems
practically this computation is eliminated in optimized builds, but this
will avoid it in O0 builds as well).

Added a unit test that demonstrates this issue by building LLVM with
these options:

```
CMAKE_BUILD_TYPE=Debug
LLVM_USE_SANITIZER=Address
LLVM_OPTIMIZE_SANITIZED_BUILDS=OFF
```

The error reported is as follows:

```
==462665==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x5030000391a2 at pc 0x56525cc30bbf bp 0x7fff9e4ccc60 sp 0x7fff9e4cc428
READ of size 19 at 0x5030000391a2 thread T0
    #0 0x56525cc30bbe in strlen (upstream-llvm-second/llvm-project/build/unittests/IR/IRTests+0x713bbe) (BuildId: 0651acf1e582a4d2)
    #1 0x7f8ff22ad334 in std::char_traits<char>::length(char const*) /usr/bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/bits/char_traits.h:399:9
    llvm#2 0x7f8ff22a34a0 in llvm::StringRef::StringRef(char const*) /home/rjoshi/upstream-llvm-second/llvm-project/llvm/include/llvm/ADT/StringRef.h:96:33
    llvm#3 0x7f8ff28ca184 in _ZZL25lookupLLVMIntrinsicByNameN4llvm8ArrayRefIjEENS_9StringRefES2_ENK3$_0clIjPKcEEDaT_T0_ upstream-llvm-second/llvm-project/llvm/lib/IR/Intrinsics.cpp:673:18
```

…lvm#148205)

In the original motivating test case,
[FoldList](https://github.com/llvm/llvm-project/blob/d8a2141ff98ee35cd1886f536ccc3548b012820b/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp#L1764)
had entries:
```
  #0: UseMI: %224:sreg_32 = S_OR_B32 %219.sub0:sreg_64, %219.sub1:sreg_64, implicit-def dead $scc
      UseOpNo: 1

  #1: UseMI: %224:sreg_32 = S_OR_B32 %219.sub0:sreg_64, %219.sub1:sreg_64, implicit-def dead $scc
      UseOpNo: 2
```
After calling
[updateOperand(#0)](https://github.com/llvm/llvm-project/blob/d8a2141ff98ee35cd1886f536ccc3548b012820b/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp#L1773),
[tryConstantFoldOp(#0.UseMI)](https://github.com/llvm/llvm-project/blob/d8a2141ff98ee35cd1886f536ccc3548b012820b/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp#L1786)
removed operand 1, and entry #&llvm#8203;1.UseOpNo was no longer valid,
resulting in an
[assert](https://github.com/llvm/llvm-project/blob/4a35214bddbb67f9597a500d48ab8c4fb25af150/llvm/include/llvm/ADT/ArrayRef.h#L452).

This change defers constant folding until all operands have been updated
so that UseOpNo values remain stable.