Added llvm lifetime annotations to function call argument temporaries.

The goal of this change is to ensure that llvm will do stack slot optimization on these temporaries. This ensures that in code like: ```rust const A: [u8; 1024] = [0; 1024]; fn copy_const() { f(A); f(A); } ``` we only use 1024 bytes of stack space, instead of 2048 bytes.

Author: davidv1992

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -132,6 +132,7 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
  llargs: &[Bx::Value],
  destination: Option<(ReturnDest<'tcx, Bx::Value>, mir::BasicBlock)>,
  cleanup: Option<mir::BasicBlock>,
+ argument_tmps: &[PlaceRef<'tcx, <Bx as BackendTypes>::Value>],
  ) {
  // If there is a cleanup block and the function we're calling can unwind, then
  // do an invoke, otherwise do a call.
@@ -172,6 +173,9 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
  if let Some((ret_dest, target)) = destination {
  bx.switch_to_block(fx.llbb(target));
  fx.set_debug_loc(bx, self.terminator.source_info);
+ for tmp in argument_tmps {
+ bx.lifetime_end(tmp.llval, tmp.layout.size);
+ }
  fx.store_return(bx, ret_dest, &fn_abi.ret, invokeret);
  }
  } else {
@@ -186,6 +190,9 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
  }
 
  if let Some((ret_dest, target)) = destination {
+ for tmp in argument_tmps {
+ bx.lifetime_end(tmp.llval, tmp.layout.size);
+ }
  fx.store_return(bx, ret_dest, &fn_abi.ret, llret);
  self.funclet_br(fx, bx, target);
  } else {
@@ -415,6 +422,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  args,
  Some((ReturnDest::Nothing, target)),
  unwind,
+ &[],
  );
  }
 
@@ -492,7 +500,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  let (fn_abi, llfn) = common::build_langcall(&bx, Some(span), lang_item);
 
  // Codegen the actual panic invoke/call.
- helper.do_call(self, &mut bx, fn_abi, llfn, &args, None, cleanup);
+ helper.do_call(self, &mut bx, fn_abi, llfn, &args, None, cleanup, &[]);
  }
 
  fn codegen_abort_terminator(
@@ -508,7 +516,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  let (fn_abi, llfn) = common::build_langcall(&bx, Some(span), LangItem::PanicNoUnwind);
 
  // Codegen the actual panic invoke/call.
- helper.do_call(self, &mut bx, fn_abi, llfn, &[], None, None);
+ helper.do_call(self, &mut bx, fn_abi, llfn, &[], None, None, &[]);
  }
 
  /// Returns `true` if this is indeed a panic intrinsic and codegen is done.
@@ -579,6 +587,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  &[msg.0, msg.1, location],
  target.as_ref().map(|bb| (ReturnDest::Nothing, *bb)),
  cleanup,
+ &[],
  );
  } else {
  // a NOP
@@ -786,6 +795,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  (args, None)
  };
 
+ let mut argument_tmps = vec![];
  'make_args: for (i, arg) in first_args.iter().enumerate() {
  let mut op = self.codegen_operand(&mut bx, arg);
 
@@ -851,8 +861,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  (&mir::Operand::Copy(_), Ref(_, None, _))
  | (&mir::Operand::Constant(_), Ref(_, None, _)) => {
  let tmp = PlaceRef::alloca(&mut bx, op.layout);
+ bx.lifetime_start(tmp.llval, tmp.layout.size);
  op.val.store(&mut bx, tmp);
  op.val = Ref(tmp.llval, None, tmp.align);
+ argument_tmps.push(tmp);
  }
  _ => {}
  }
@@ -925,6 +937,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  &llargs,
  target.as_ref().map(|&target| (ret_dest, target)),
  cleanup,
+ &argument_tmps,
  );
 
  bx.switch_to_block(bb_fail);
@@ -942,6 +955,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  &llargs,
  target.as_ref().map(|&target| (ret_dest, target)),
  cleanup,
+ &argument_tmps,
  );
  }