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[AVR] Do not clear r0 at interrupt entry 

There is no reason to do this: it's a scratch register and can therefore
hold any arbitrary value. And because it is in an interrupt, this code
is performance critical so it should be as short as possible.

I believe r0 was cleared because of the following:

 1. There used to be a bug that the cleared register was r0, not r1 as
    it should have been.
 2. This was fixed in https://reviews.llvm.org/D99467, but left the code
    to clear r0.

This patch completes D99467 by removing the `clr r0` instruction.

Differential Revision: https://reviews.llvm.org/D116756
This commit is contained in:
Ayke van Laethem 2022-01-06 18:22:06 +01:00
parent 3d59d94a20
commit ca27b026f9
No known key found for this signature in database
GPG Key ID: E97FF5335DFDFDED
2 changed files with 0 additions and 12 deletions
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5
llvm/lib/Target/AVR/AVRFrameLowering.cpp
View File

@ -78,11 +78,6 @@ void AVRFrameLowering::emitPrologue(MachineFunction &MF,
BuildMI(MBB, MBBI, DL, TII.get(AVR::PUSHRr))
.addReg(AVR::R0, RegState::Kill)
.setMIFlag(MachineInstr::FrameSetup);
BuildMI(MBB, MBBI, DL, TII.get(AVR::EORRdRr))
.addReg(AVR::R0, RegState::Define)
.addReg(AVR::R0, RegState::Kill)
.addReg(AVR::R0, RegState::Kill)
.setMIFlag(MachineInstr::FrameSetup);
BuildMI(MBB, MBBI, DL, TII.get(AVR::EORRdRr))
.addReg(AVR::R1, RegState::Define)
.addReg(AVR::R1, RegState::Kill)

7
llvm/test/CodeGen/AVR/interrupts.ll
View File

@ -9,7 +9,6 @@ define avr_intrcc void @interrupt_handler() {
; CHECK-NEXT: push r1
; CHECK-NEXT: in r0, 63
; CHECK-NEXT: push r0
; CHECK: clr r0
; CHECK-NEXT: clr r1
; CHECK: pop r0
; CHECK-NEXT: out 63, r0
@ -26,7 +25,6 @@ define void @interrupt_handler_via_ir_attribute() #0 {
; CHECK-NEXT: push r1
; CHECK-NEXT: in r0, 63
; CHECK-NEXT: push r0
; CHECK: clr r0
; CHECK-NEXT: clr r1
; CHECK: pop r0
; CHECK-NEXT: out 63, r0
@ -43,7 +41,6 @@ define avr_signalcc void @signal_handler() {
; CHECK-NEXT: push r1
; CHECK-NEXT: in r0, 63
; CHECK-NEXT: push r0
; CHECK: clr r0
; CHECK-NEXT: clr r1
; CHECK: pop r0
; CHECK-NEXT: out 63, r0
@ -60,7 +57,6 @@ define void @signal_handler_via_attribute() #1 {
; CHECK-NEXT: push r1
; CHECK-NEXT: in r0, 63
; CHECK-NEXT: push r0
; CHECK: clr r0
; CHECK-NEXT: clr r1
; CHECK: pop r0
; CHECK-NEXT: out 63, r0
@ -77,7 +73,6 @@ define avr_intrcc void @interrupt_alloca() {
; CHECK-NEXT: push r1
; CHECK-NEXT: in r0, 63
; CHECK-NEXT: push r0
; CHECK: clr r0
; CHECK-NEXT: clr r1
; CHECK: push r28
; CHECK-NEXT: push r29
@ -112,7 +107,6 @@ define void @signal_handler_with_increment() #1 {
; CHECK-NEXT: push r1
; CHECK-NEXT: in r0, 63
; CHECK-NEXT: push r0
; CHECK-NEXT: clr r0
; CHECK-NEXT: clr r1
; CHECK-NEXT: push r24
; CHECK-NEXT: lds r24, count
@ -140,7 +134,6 @@ define void @signal_handler_with_call() #1 {
; CHECK-NEXT: push r1
; CHECK-NEXT: in r0, 63
; CHECK-NEXT: push r0
; CHECK-NEXT: clr r0
; CHECK-NEXT: clr r1
; CHECK-NEXT: push r18
; CHECK-NEXT: push r19