[PATCH] D97128: [ThinLTO] Make cloneUsedGlobalVariables deterministic

[Fangrui Song via Phabricator via llvm-commits]

MaskRay updated this revision to Diff 325876.
MaskRay edited the summary of this revision.
MaskRay added a comment.

Explain that we decrease the inline element count to 4.
(This can make clang smaller due to fewer instantiations.)


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D97128/new/

https://reviews.llvm.org/D97128

Files:
  llvm/include/llvm/IR/Module.h
  llvm/lib/IR/Module.cpp
  llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp


Index: llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
===================================================================
--- llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
+++ llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
@@ -199,23 +199,20 @@
 // values whose defs were cloned into that module.
 static void cloneUsedGlobalVariables(const Module &SrcM, Module &DestM,
                                      bool CompilerUsed) {
-  SmallPtrSet<GlobalValue *, 8> Used;
-  SmallPtrSet<GlobalValue *, 8> NewUsed;
+  SmallVector<GlobalValue *, 4> Used, NewUsed;
   // First collect those in the llvm[.compiler].used set.
   collectUsedGlobalVariables(SrcM, Used, CompilerUsed);
   // Next build a set of the equivalent values defined in DestM.
   for (auto *V : Used) {
     auto *GV = DestM.getNamedValue(V->getName());
     if (GV && !GV->isDeclaration())
-      NewUsed.insert(GV);
+      NewUsed.push_back(GV);
   }
   // Finally, add them to a llvm[.compiler].used variable in DestM.
   if (CompilerUsed)
-    appendToCompilerUsed(
-        DestM, std::vector<GlobalValue *>(NewUsed.begin(), NewUsed.end()));
+    appendToCompilerUsed(DestM, NewUsed);
   else
-    appendToUsed(DestM,
-                 std::vector<GlobalValue *>(NewUsed.begin(), NewUsed.end()));
+    appendToUsed(DestM, NewUsed);
 }
 
 // If it's possible to split M into regular and thin LTO parts, do so and write
Index: llvm/lib/IR/Module.cpp
===================================================================
--- llvm/lib/IR/Module.cpp
+++ llvm/lib/IR/Module.cpp
@@ -658,6 +658,21 @@
   return Result;
 }
 
+GlobalVariable *llvm::collectUsedGlobalVariables(
+    const Module &M, SmallVectorImpl<GlobalValue *> &Set, bool CompilerUsed) {
+  const char *Name = CompilerUsed ? "llvm.compiler.used" : "llvm.used";
+  GlobalVariable *GV = M.getGlobalVariable(Name);
+  if (!GV || !GV->hasInitializer())
+    return GV;
+
+  const ConstantArray *Init = cast<ConstantArray>(GV->getInitializer());
+  for (Value *Op : Init->operands()) {
+    GlobalValue *G = cast<GlobalValue>(Op->stripPointerCasts());
+    Set.push_back(G);
+  }
+  return GV;
+}
+
 GlobalVariable *llvm::collectUsedGlobalVariables(
     const Module &M, SmallPtrSetImpl<GlobalValue *> &Set, bool CompilerUsed) {
   const char *Name = CompilerUsed ? "llvm.compiler.used" : "llvm.used";
Index: llvm/include/llvm/IR/Module.h
===================================================================
--- llvm/include/llvm/IR/Module.h
+++ llvm/include/llvm/IR/Module.h
@@ -890,6 +890,9 @@
 
 /// Given "llvm.used" or "llvm.compiler.used" as a global name, collect
 /// the initializer elements of that global in Set and return the global itself.
+GlobalVariable *collectUsedGlobalVariables(const Module &M,
+                                           SmallVectorImpl<GlobalValue *> &Set,
+                                           bool CompilerUsed);
 GlobalVariable *collectUsedGlobalVariables(const Module &M,
                                            SmallPtrSetImpl<GlobalValue *> &Set,
                                            bool CompilerUsed);


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