compiler-rt/lib/builtins/hexagon/common_entry_exit_abi1.S

//===----------------------Hexagon builtin routine ------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// Functions that implement common sequences in function prologues and epilogues
// used to save code size

	.macro FUNCTION_BEGIN name
	.text
	.globl \name
	.type  \name, @function
	.falign
\name:
	.endm

	.macro FUNCTION_END name
	.size  \name, . - \name
	.endm

	.macro FALLTHROUGH_TAIL_CALL name0 name1
	.size \name0, . - \name0
	.globl \name1
	.type \name1, @function
	.falign
\name1:
	.endm




// Save r25:24 at fp+#-8 and r27:26 at fp+#-16.




// The compiler knows that the __save_* functions clobber LR.  No other
// registers should be used without informing the compiler.

// Since we can only issue one store per packet, we don't hurt performance by
// simply jumping to the right point in this sequence of stores.

FUNCTION_BEGIN __save_r24_through_r27
		memd(fp+#-16) = r27:26
FALLTHROUGH_TAIL_CALL __save_r24_through_r27 __save_r24_through_r25
	{
		memd(fp+#-8) = r25:24
		jumpr lr
	}
FUNCTION_END __save_r24_through_r25




// For each of the *_before_tailcall functions, jumpr lr is executed in parallel
// with deallocframe.  That way, the return gets the old value of lr, which is
// where these functions need to return, and at the same time, lr gets the value
// it needs going into the tail call.

FUNCTION_BEGIN __restore_r24_through_r27_and_deallocframe_before_tailcall
		r27:26 = memd(fp+#-16)
FALLTHROUGH_TAIL_CALL __restore_r24_through_r27_and_deallocframe_before_tailcall __restore_r24_through_r25_and_deallocframe_before_tailcall
	{
		r25:24 = memd(fp+#-8)
		deallocframe
		jumpr lr
	}
FUNCTION_END __restore_r24_through_r25_and_deallocframe_before_tailcall




// Here we use the extra load bandwidth to restore LR early, allowing the return
// to occur in parallel with the deallocframe.

FUNCTION_BEGIN __restore_r24_through_r27_and_deallocframe
	{
		lr = memw(fp+#4)
		r27:26 = memd(fp+#-16)
	}
	{
		r25:24 = memd(fp+#-8)
		deallocframe
		jumpr lr
	}
FUNCTION_END __restore_r24_through_r27_and_deallocframe




// Here the load bandwidth is maximized.

FUNCTION_BEGIN __restore_r24_through_r25_and_deallocframe
	{
		r25:24 = memd(fp+#-8)
		deallocframe
	}
		jumpr lr
FUNCTION_END __restore_r24_through_r25_and_deallocframe