[PATCH] D78929: [AIX][XCOFF]emit extern linkage for the llvm intrinsic symbol

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1. when we call memset, memcopy,memmove etc(this are llvm intrinsic function) in the c source code. the llvm will generate IR

like call call void @llvm.memset.p0i8.i32(i8* align 4 bitcast (%struct.S* @s to i8*), i8 %1, i32 %2, i1 false)
for c source code
bash> cat test_memset.call

  struct S{
   int a;
   int b;
  };
  extern struct  S s;
  void bar() {
    memset(&s, s.b, s.b);
  }

like

  %struct.S = type { i32, i32 }
  @s = external global %struct.S, align 4
  ; Function Attrs: noinline nounwind optnone
  define void @bar() #0 {
  entry:
    %0 = load i32, i32* getelementptr inbounds (%struct.S, %struct.S* @s, i32 0, i32 1), align 4
    %1 = trunc i32 %0 to i8
    %2 = load i32, i32* getelementptr inbounds (%struct.S, %struct.S* @s, i32 0, i32 1), align 4
    call void @llvm.memset.p0i8.i32(i8* align 4 bitcast (%struct.S* @s to i8*), i8 %1, i32 %2, i1 false)
    ret void
  }

declare void @llvm.memset.p0i8.i32(i8* nocapture writeonly, i8, i32, i1 immarg) #1
If we want to let the aix as assembly compile pass without -u
it need to has following assembly code.
.extern .memset
(we do not output extern linkage for llvm instrinsic function.
even if we output the extern linkage for llvm intrinsic function, we should not out .extern llvm.memset.p0i8.i32,
instead of we should emit .extern memset)

2. for other llvm buildin function  __floatdidf .  even if we do not call these function  __floatdidf  in the c source code(the generated IR also do not the call  __floatdidf . the function call

was generated in the LLVM optimized.
the function is not in the functions list of Module, but we still need to emit extern .__floatdidf

The solution for it as :
We record all the lllvm intrinsic extern symbol when transformCallee(), and emit all these symbol in the  AsmPrinter::doFinalization(Module &M)


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D78929

Files:
  llvm/include/llvm/MC/MCContext.h
  llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
  llvm/lib/MC/MCContext.cpp
  llvm/lib/Target/PowerPC/PPCISelLowering.cpp
  llvm/test/CodeGen/PowerPC/aix-llvm-intrinsic.ll

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