Commit 35c63d66 authored by Amara Emerson's avatar Amara Emerson
Browse files

[GlobalISel][CallLowering] Look through bitcasts from constant function pointers. 

Calls to ObjC's objc_msgSend function are done by bitcasting the function global
to the required function type signature. This patch looks through this bitcast
so that we can do a direct call with bl on arm64 instead of using an indirect blr.

Differential Revision: https://reviews.llvm.org/D74241
parent fbb4d1e4

llvm/lib/CodeGen/GlobalISel/CallLowering.cpp

+12 −2
Original line number Diff line number Diff line
@@ -52,8 +52,18 @@ bool CallLowering::lowerCall(MachineIRBuilder &MIRBuilder, ImmutableCallSite CS, 


  if (const Function *F = CS.getCalledFunction())

    Info.Callee = MachineOperand::CreateGA(F, 0);

  else

  else {

    // Try looking through a bitcast from one function type to another.

    // Commonly happens with calls to objc_msgSend().

    const Value *CalleeV = CS.getCalledValue();

    if (auto *BC = dyn_cast<ConstantExpr>(CalleeV)) {

      if (const auto *F = dyn_cast<Function>(BC->getOperand(0))) {

        Info.Callee = MachineOperand::CreateGA(F, 0);

      }

    } else {

      Info.Callee = MachineOperand::CreateReg(GetCalleeReg(), false);

    }

  }



  Info.OrigRet = ArgInfo{ResRegs, CS.getType(), ISD::ArgFlagsTy{}};

  if (!Info.OrigRet.Ty->isVoidTy())

llvm/test/CodeGen/AArch64/GlobalISel/call-lowering-const-bitcast-func.ll

0 → 100644
+14 −0
Original line number Diff line number Diff line 
; RUN: llc -O0 -global-isel -verify-machineinstrs %s -o - 2>&1 | FileCheck %s



target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"

target triple = "aarch64-darwin-ios13.0"



declare i8* @objc_msgSend(i8*, i8*, ...)

define void @call_bitcast_ptr_const() {

; CHECK-LABEL: @call_bitcast_ptr_const

; CHECK: bl _objc_msgSend

; CHECK-NOT: blr

entry:

  call void bitcast (i8* (i8*, i8*, ...)* @objc_msgSend to void (i8*, i8*, [2 x i32], i32, float)*)(i8* undef, i8* undef, [2 x i32] zeroinitializer, i32 0, float 1.000000e+00)

  ret void

}