[PtrAuth] Add ConstantPtrAuth comparator to FunctionComparator.cpp (#159480)

When building rustc std for arm64e, core fails to compile successfully
with the error:
```
Constant ValueID not recognized.
UNREACHABLE executed at rust/src/llvm-project/llvm/lib/Transforms/Utils/FunctionComparator.cpp:523!
```

This is a result of function merging so I modified
FunctionComparator.cpp as the ConstantPtrAuth value would go unchecked
in the switch statement.

The test case is a reduction from the failure in core and fails on main
with:
```
********************
FAIL: LLVM :: Transforms/MergeFunc/ptrauth-const-compare.ll (59809 of 59995)
******************** TEST 'LLVM :: Transforms/MergeFunc/ptrauth-const-compare.ll' FAILED ********************
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 3
/Users/oskarwirga/llvm-project/build/bin/opt -S -passes=mergefunc < /Users/oskarwirga/llvm-project/llvm/test/Transforms/MergeFunc/ptrauth-const-compare.ll | /Users/oskarwirga/llvm-project/build/bin/FileCheck /Users/oskarwirga/llvm-project/llvm/test/Transforms/MergeFunc/ptrauth-const-compare.ll
# executed command: /Users/oskarwirga/llvm-project/build/bin/opt -S -passes=mergefunc
# .---command stderr------------
# | Constant ValueID not recognized.
# | UNREACHABLE executed at /Users/oskarwirga/llvm-project/llvm/lib/Transforms/Utils/FunctionComparator.cpp:523!
# | PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and instructions to reproduce the bug.
# | Stack dump:
# | 0.	Program arguments: /Users/oskarwirga/llvm-project/build/bin/opt -S -passes=mergefunc
# | 1.	Running pass "mergefunc" on module "<stdin>"
# |  #0 0x0000000103335770 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/Users/oskarwirga/llvm-project/build/bin/opt+0x102651770)
# |  #1 0x00000001033336bc llvm::sys::RunSignalHandlers() (/Users/oskarwirga/llvm-project/build/bin/opt+0x10264f6bc)
# |  #2 0x0000000103336218 SignalHandler(int, __siginfo*, void*) (/Users/oskarwirga/llvm-project/build/bin/opt+0x102652218)
# |  #3 0x000000018e6c16a4 (/usr/lib/system/libsystem_platform.dylib+0x1804ad6a4)
# |  #4 0x000000018e68788c (/usr/lib/system/libsystem_pthread.dylib+0x18047388c)
# |  #5 0x000000018e590a3c (/usr/lib/system/libsystem_c.dylib+0x18037ca3c)
# |  #6 0x00000001032a84bc llvm::install_out_of_memory_new_handler() (/Users/oskarwirga/llvm-project/build/bin/opt+0x1025c44bc)
# |  #7 0x00000001033b37c0 llvm::FunctionComparator::cmpMDNode(llvm::MDNode const*, llvm::MDNode const*) const (/Users/oskarwirga/llvm-project/build/bin/opt+0x1026cf7c0)
# |  #8 0x00000001033b4d90 llvm::FunctionComparator::cmpBasicBlocks(llvm::BasicBlock const*, llvm::BasicBlock const*) const (/Users/oskarwirga/llvm-project/build/bin/opt+0x1026d0d90)
# |  #9 0x00000001033b5234 llvm::FunctionComparator::compare() (/Users/oskarwirga/llvm-project/build/bin/opt+0x1026d1234)
# | #10 0x0000000102d6d868 (anonymous namespace)::MergeFunctions::insert(llvm::Function*) (/Users/oskarwirga/llvm-project/build/bin/opt+0x102089868)
# | #11 0x0000000102d6bc0c llvm::MergeFunctionsPass::runOnModule(llvm::Module&) (/Users/oskarwirga/llvm-project/build/bin/opt+0x102087c0c)
# | #12 0x0000000102d6b430 llvm::MergeFunctionsPass::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/Users/oskarwirga/llvm-project/build/bin/opt+0x102087430)
# | #13 0x0000000102b90558 llvm::PassManager<llvm::Module, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/Users/oskarwirga/llvm-project/build/bin/opt+0x101eac558)
# | #14 0x0000000103734bc4 llvm::runPassPipeline(llvm::StringRef, llvm::Module&, llvm::TargetMachine*, llvm::TargetLibraryInfoImpl*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::StringRef, llvm::ArrayRef<llvm::PassPlugin>, llvm::ArrayRef<std::__1::function<void (llvm::PassBuilder&)>>, llvm::opt_tool::OutputKind, llvm::opt_tool::VerifierKind, bool, bool, bool, bool, bool, bool, bool, bool) (/Users/oskarwirga/llvm-project/build/bin/opt+0x102a50bc4)
# | #15 0x000000010373cc28 optMain (/Users/oskarwirga/llvm-project/build/bin/opt+0x102a58c28)
# | #16 0x000000018e2e6b98
# `-----------------------------
# error: command failed with exit status: -6
# executed command: /Users/oskarwirga/llvm-project/build/bin/FileCheck /Users/oskarwirga/llvm-project/llvm/test/Transforms/MergeFunc/ptrauth-const-compare.ll
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  /Users/oskarwirga/llvm-project/build/bin/FileCheck /Users/oskarwirga/llvm-project/llvm/test/Transforms/MergeFunc/ptrauth-const-compare.ll
# `-----------------------------
# error: command failed with exit status: 2
```

Author: oskarwirga

llvm/lib/Transforms/Utils/FunctionComparator.cpp

@@ -518,6 +518,20 @@ int FunctionComparator::cmpConstants(const Constant *L,
     const auto *REquiv = cast<DSOLocalEquivalent>(R);
     return cmpGlobalValues(LEquiv->getGlobalValue(), REquiv->getGlobalValue());
   }
+  case Value::ConstantPtrAuthVal: {
+    // Handle authenticated pointer constants produced by ConstantPtrAuth::get.
+    const ConstantPtrAuth *LPA = cast<ConstantPtrAuth>(L);
+    const ConstantPtrAuth *RPA = cast<ConstantPtrAuth>(R);
+    if (int Res = cmpConstants(LPA->getPointer(), RPA->getPointer()))
+      return Res;
+    if (int Res = cmpConstants(LPA->getKey(), RPA->getKey()))
+      return Res;
+    if (int Res =
+            cmpConstants(LPA->getDiscriminator(), RPA->getDiscriminator()))
+      return Res;
+    return cmpConstants(LPA->getAddrDiscriminator(),
+                        RPA->getAddrDiscriminator());
+  }
   default: // Unknown constant, abort.
     LLVM_DEBUG(dbgs() << "Looking at valueID " << L->getValueID() << "\n");
     llvm_unreachable("Constant ValueID not recognized.");

llvm/test/Transforms/MergeFunc/ptrauth-const-compare.ll

@@ -0,0 +1,133 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt -passes=mergefunc -S < %s | FileCheck %s
+; Ensure MergeFunc handles ConstantPtrAuth correctly and does not
+; merge when any ptrauth operand differs (ptr, key, int disc, addr disc).
+; Each pair of functions differs only in a single ptrauth component but shares
+; the same return value, so disabling any single comparison would cause a
+; test failure due to unexpected merging.
+
+target triple = "arm64e-apple-ios14.0.0"
+
+declare void @baz()
+@ADDR = external global i8
+
+declare void @callee(ptr)
+
+; different base pointer (null vs @baz)
+
+define i32 @f_ptr_null() {
+; CHECK-LABEL: define i32 @f_ptr_null() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    call void @callee(ptr ptrauth (ptr null, i32 0))
+; CHECK-NEXT:    ret i32 1
+;
+entry:
+  call void @callee(ptr ptrauth (ptr null, i32 0))
+  ret i32 1
+}
+
+define i32 @g_ptr_baz() {
+; CHECK-LABEL: define i32 @g_ptr_baz() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    call void @callee(ptr ptrauth (ptr @baz, i32 0))
+; CHECK-NEXT:    ret i32 1
+;
+entry:
+  call void @callee(ptr ptrauth (ptr @baz, i32 0))
+  ret i32 1
+}
+
+; different key (i32 0 vs i32 1)
+
+define i32 @f_key0() {
+; CHECK-LABEL: define i32 @f_key0() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    call void @callee(ptr ptrauth (ptr @baz, i32 0))
+; CHECK-NEXT:    ret i32 2
+;
+entry:
+  call void @callee(ptr ptrauth (ptr @baz, i32 0))
+  ret i32 2
+}
+
+define i32 @g_key1() {
+; CHECK-LABEL: define i32 @g_key1() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    call void @callee(ptr ptrauth (ptr @baz, i32 1))
+; CHECK-NEXT:    ret i32 2
+;
+entry:
+  call void @callee(ptr ptrauth (ptr @baz, i32 1))
+  ret i32 2
+}
+
+; different integer disc (i64 0 vs i64 7)
+
+define i32 @f_disc0() {
+; CHECK-LABEL: define i32 @f_disc0() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    call void @callee(ptr ptrauth (ptr @baz, i32 0))
+; CHECK-NEXT:    ret i32 3
+;
+entry:
+  call void @callee(ptr ptrauth (ptr @baz, i32 0))
+  ret i32 3
+}
+
+define i32 @g_disc7() {
+; CHECK-LABEL: define i32 @g_disc7() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    call void @callee(ptr ptrauth (ptr @baz, i32 0, i64 7))
+; CHECK-NEXT:    ret i32 3
+;
+entry:
+  call void @callee(ptr ptrauth (ptr @baz, i32 0, i64 7))
+  ret i32 3
+}
+
+; different addr disc (ptr null vs @ADDR)
+
+define i32 @f_addr_null() {
+; CHECK-LABEL: define i32 @f_addr_null() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    call void @callee(ptr ptrauth (ptr @baz, i32 0))
+; CHECK-NEXT:    ret i32 4
+;
+entry:
+  call void @callee(ptr ptrauth (ptr @baz, i32 0))
+  ret i32 4
+}
+
+define i32 @g_addr_ADDR() {
+; CHECK-LABEL: define i32 @g_addr_ADDR() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    call void @callee(ptr ptrauth (ptr @baz, i32 0, i64 0, ptr @ADDR))
+; CHECK-NEXT:    ret i32 4
+;
+entry:
+  call void @callee(ptr ptrauth (ptr @baz, i32 0, i64 0, ptr @ADDR))
+  ret i32 4
+}
+
+; positive test: identical ptrauth operands, should be merged
+
+define void @merge_ptrauth_a() {
+; CHECK-LABEL: define void @merge_ptrauth_a() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    call void @callee(ptr ptrauth (ptr @baz, i32 0, i64 0, ptr @ADDR))
+; CHECK-NEXT:    ret void
+;
+entry:
+  call void @callee(ptr ptrauth (ptr @baz, i32 0, i64 0, ptr @ADDR))
+  ret void
+}
+
+define void @merge_ptrauth_b() {
+; CHECK-LABEL: define void @merge_ptrauth_b() {
+; CHECK-NEXT:    tail call void @merge_ptrauth_a()
+; CHECK-NEXT:    ret void
+;
+entry:
+  call void @callee(ptr ptrauth (ptr @baz, i32 0, i64 0, ptr @ADDR))
+  ret void
+}