[PATCH] D153197: [AVR] Expand shifts during AVRISelLowering

[Patryk Wychowaniec via Phabricator via cfe-commits]

Patryk27 added inline comments.


================
Comment at: llvm/lib/Target/AVR/AVRISelLowering.cpp:2193
+// (the output registers are stored in this array on return).
+static MachineBasicBlock *insertMultibyteShiftLoop(
+    MachineInstr &MI, MachineBasicBlock *BB, Register ShiftNum,
----------------
Note that I've changed to code to re-arrange the generated blocks a bit, from:

```
body:             |
  bb.0 (%ir-block.0):
    successors: %bb.2(0x80000000)
    liveins: $r23r22, $r25r24, $r19r18
  
    %2:dregs = COPY $r19r18
    %1:dregs = COPY $r25r24
    %0:dregs = COPY $r23r22
    %4:gpr8 = COPY %2.sub_lo
    RJMPk %bb.2
  
  bb.1 (%ir-block.0):
    successors: %bb.2(0x80000000)
  
    %12:gpr8 = ADDRdRr %10, %10, implicit-def $sreg
    %13:gpr8 = ADCRdRr %9, %9, implicit-def $sreg, implicit $sreg
    %14:gpr8 = ADCRdRr %8, %8, implicit-def $sreg, implicit $sreg
    %15:gpr8 = ADCRdRr %7, %7, implicit-def $sreg, implicit $sreg
  
  bb.2 (%ir-block.0):
    successors: %bb.1(0x40000000), %bb.3(0x40000000)
  
    %7:gpr8 = PHI %1.sub_hi, %bb.0, %15, %bb.1
    %8:gpr8 = PHI %1.sub_lo, %bb.0, %14, %bb.1
    %9:gpr8 = PHI %0.sub_hi, %bb.0, %13, %bb.1
    %10:gpr8 = PHI %0.sub_lo, %bb.0, %12, %bb.1
    %16:gpr8 = PHI %4, %bb.0, %17, %bb.1
    %17:gpr8 = DECRd %16, implicit-def $sreg
    BRPLk %bb.1, implicit $sreg
  
  bb.3 (%ir-block.0):
    %6:dregs = REG_SEQUENCE %7, %subreg.sub_hi, %8, %subreg.sub_lo
    %5:dregs = REG_SEQUENCE %9, %subreg.sub_hi, %10, %subreg.sub_lo
    $r23r22 = COPY %5
    $r25r24 = COPY %6
    RET implicit $r23r22, implicit $r25r24, implicit $r1
```

... to:

```
body:             |
  bb.0 (%ir-block.0):
    successors: %bb.1(0x80000000)
    liveins: $r23r22, $r25r24, $r19r18
  
    %2:dregs = COPY $r19r18
    %1:dregs = COPY $r25r24
    %0:dregs = COPY $r23r22
    %4:gpr8 = COPY %2.sub_lo
    # fall-through instead of jumping
  
  bb.1 (%ir-block.0):
    successors: %bb.2(0x40000000), %bb.3(0x40000000)
  
    %7:gpr8 = PHI %1.sub_hi, %bb.0, %15, %bb.2
    %8:gpr8 = PHI %1.sub_lo, %bb.0, %14, %bb.2
    %9:gpr8 = PHI %0.sub_hi, %bb.0, %13, %bb.2
    %10:gpr8 = PHI %0.sub_lo, %bb.0, %12, %bb.2
    %16:gpr8 = PHI %4, %bb.0, %17, %bb.2
    %17:gpr8 = DECRd %16, implicit-def $sreg
    BRMIk %bb.3, implicit $sreg # <- reversed comparison + fallthrough
  
  bb.2 (%ir-block.0):
    successors: %bb.1(0x80000000)
  
    %12:gpr8 = ADDRdRr %10, %10, implicit-def $sreg
    %13:gpr8 = ADCRdRr %9, %9, implicit-def $sreg, implicit $sreg
    %14:gpr8 = ADCRdRr %8, %8, implicit-def $sreg, implicit $sreg
    %15:gpr8 = ADCRdRr %7, %7, implicit-def $sreg, implicit $sreg
    RJMPk %bb.1 # <- jump to the beginning
  
  bb.3 (%ir-block.0):
    %6:dregs = REG_SEQUENCE %7, %subreg.sub_hi, %8, %subreg.sub_lo
    %5:dregs = REG_SEQUENCE %9, %subreg.sub_hi, %10, %subreg.sub_lo
    $r23r22 = COPY %5
    $r25r24 = COPY %6
    RET implicit $r23r22, implicit $r25r24, implicit $r1
```

It looks like the generated assembly remained the same, I've also checked the actual binary through rustc + simavr.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D153197/new/

https://reviews.llvm.org/D153197