[PATCH] D135799: libcxxabi [PR58117][NFC]: Open code lower bound

[Nathan Sidwell via Phabricator via llvm-commits]

urnathan created this revision.
urnathan added reviewers: libc++abi, arichardson.
Herald added a project: All.
urnathan requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

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.


https://reviews.llvm.org/D135799

Files:
  libcxxabi/src/demangle/ItaniumDemangle.h
  llvm/include/llvm/Demangle/ItaniumDemangle.h


Index: llvm/include/llvm/Demangle/ItaniumDemangle.h
===================================================================
--- llvm/include/llvm/Demangle/ItaniumDemangle.h
+++ llvm/include/llvm/Demangle/ItaniumDemangle.h
@@ -3032,14 +3032,21 @@
   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()
Index: libcxxabi/src/demangle/ItaniumDemangle.h
===================================================================
--- libcxxabi/src/demangle/ItaniumDemangle.h
+++ libcxxabi/src/demangle/ItaniumDemangle.h
@@ -3032,14 +3032,21 @@
   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()


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D135799.467200.patch
Type: text/x-patch
Size: 1974 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20221012/32ad6919/attachment.bin>