libcxxabi [PR58117][NFC]: Open code lower bound

This open codes the use of lower-bound when looking for an operator
encoding. Using std::lower_bound can result in symbol references to
the C++ library and that breaks the ABI demangler, which mandates no
such dependency.

Differential Revision: https://reviews.llvm.org/D135799

Fixes: https://github.com/llvm/llvm-project/issues/58117

1 files changed, 12 insertions, 5 deletions

diff --git a/libcxxabi/src/demangle/ItaniumDemangle.h b/libcxxabi/src/demangle/ItaniumDemangle.h
index fa121cc1f325..339982584f5f 100644
--- a/libcxxabi/src/demangle/ItaniumDemangle.h
+++ b/libcxxabi/src/demangle/ItaniumDemangle.h
@@ -3032,14 +3032,21 @@ AbstractManglingParser<Derived, Alloc>::parseOperatorEncoding() {
   if (numLeft() < 2)
     return nullptr;
 
-  auto Op = std::lower_bound(
-      &Ops[0], &Ops[NumOps], First,
-      [](const OperatorInfo &Op_, const char *Enc_) { return Op_ < Enc_; });
-  if (Op == &Ops[NumOps] || *Op != First)
+  // We can't use lower_bound as that can link to symbols in the C++ library,
+  // and this must remain independant of that.
+  size_t lower = 0u, upper = NumOps - 1; // Inclusive bounds.
+  while (upper != lower) {
+    size_t middle = (upper + lower) / 2;
+    if (Ops[middle] < First)
+      lower = middle + 1;
+    else
+      upper = middle;
+  }
+  if (Ops[lower] != First)
     return nullptr;
 
   First += 2;
-  return Op;
+  return &Ops[lower];
 }
 
 //   <operator-name> ::= See parseOperatorEncoding()