[CodeGen] Don't codegen the weak function when there is a defined non-weak symbol

Author: dianqk

llvm/include/llvm/MC/MCSymbol.h

@@ -104,6 +104,9 @@ class MCSymbol {
   /// This symbol is weak external.
   mutable unsigned IsWeakExternal : 1;
 
+  /// This symbol is weak.
+  mutable unsigned IsWeak : 1;
+
   /// LLVM RTTI discriminator. This is actually a SymbolKind enumerator, but is
   /// unsigned to avoid sign extension and achieve better bitpacking with MSVC.
   unsigned Kind : 3;
@@ -163,7 +166,7 @@ class MCSymbol {
   MCSymbol(SymbolKind Kind, const StringMapEntry<bool> *Name, bool isTemporary)
       : IsTemporary(isTemporary), IsRedefinable(false), IsUsed(false),
         IsRegistered(false), IsExternal(false), IsPrivateExtern(false),
-        IsWeakExternal(false), Kind(Kind), IsUsedInReloc(false),
+        IsWeakExternal(false), IsWeak(false), Kind(Kind), IsUsedInReloc(false),
         SymbolContents(SymContentsUnset), CommonAlignLog2(0), Flags(0) {
     Offset = 0;
     HasName = !!Name;
@@ -411,6 +414,9 @@ class MCSymbol {
 
   bool isWeakExternal() const { return IsWeakExternal; }
 
+  bool isWeak() const { return IsWeak; }
+  void setWeak(bool Value) const { IsWeak = Value; }
+
   /// print - Print the value to the stream \p OS.
   void print(raw_ostream &OS, const MCAsmInfo *MAI) const;
 

llvm/lib/CodeGen/MachineFunctionPass.cpp

@@ -27,6 +27,7 @@
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/PrintPasses.h"
+#include "llvm/Target/TargetMachine.h"
 
 using namespace llvm;
 using namespace ore;
@@ -43,6 +44,12 @@ bool MachineFunctionPass::runOnFunction(Function &F) {
     return false;
 
   MachineModuleInfo &MMI = getAnalysis<MachineModuleInfoWrapperPass>().getMMI();
+  const TargetMachine &TM = MMI.getTarget();
+  MCSymbol *Symbol = TM.getSymbol(&F);
+  // Don't codegen the weak function when there is a defined non-weak symbol.
+  if (Symbol->isDefined() && !Symbol->isWeak() && F.hasWeakLinkage()) {
+    return false;
+  }
   MachineFunction &MF = MMI.getOrCreateMachineFunction(F);
 
   MachineFunctionProperties &MFProps = MF.getProperties();

llvm/lib/MC/MCParser/ELFAsmParser.cpp

@@ -189,6 +189,8 @@ bool ELFAsmParser::ParseDirectiveSymbolAttribute(StringRef Directive, SMLoc) {
 
       MCSymbol *Sym = getContext().getOrCreateSymbol(Name);
 
+      if (Attr == MCSA_Weak)
+        Sym->setWeak(true);
       getStreamer().emitSymbolAttribute(Sym, Attr);
 
       if (getLexer().is(AsmToken::EndOfStatement))

llvm/test/CodeGen/Thumb/asm-fn-weak.ll

@@ -1,14 +1,17 @@
-; RUN: not llc -mtriple=thumbv6m-none-unknown-eabi < %s 2>&1 | FileCheck %s
-
-; CHECK: error: symbol '__aeabi_uidivmod' is already defined
-; FIXME: We want to discard the weak function.
+; RUN: llc -mtriple=thumbv6m-none-unknown-eabi < %s | FileCheck %s
 
+; CHECK: .globl	__aeabi_uidivmod
+; CHECK-NEXT: .type	__aeabi_uidivmod,%function
+; CHECK-NEXT: __aeabi_uidivmod:
+; CHECK-NEXT: str	r0, [r2, #96]
+; CHECK-NEXT: str	r1, [r2, #100]
 module asm ".global __aeabi_uidivmod"
 module asm ".type __aeabi_uidivmod, %function"
 module asm "__aeabi_uidivmod:"
 module asm "str    r0, [r2, #0x060]"
 module asm "str    r1, [r2, #0x064]"
 
+; CHECK-NOT: __aeabi_uidivmod
 define weak void @__aeabi_uidivmod() #0 {
   tail call void asm sideeffect alignstack "push {lr}\0Asub sp, sp, #4\0Amov r2, sp\0Abl __udivmodsi4\0Aldr r1, [sp]\0Aadd sp, sp, #4\0Apop {pc}", "~{cc},~{memory}"()
   unreachable