[llvm] [AMDGPU] Change SGPR layout to striped caller/callee saved (PR #127353)

[Mikael Holmén via llvm-commits]

mikaelholmen wrote:

So, with this patch e.g.
```
llc -verify-machineinstrs -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 < test/CodeGen/AMDGPU/materialize-frame-index-sgpr.gfx10.ll
```
fails with
```
# After Greedy Register Allocator
********** INTERVALS **********
SGPR59_LO16 [96r,96d:0) 0 at 96r
SGPR59_HI16 [96r,96d:0) 0 at 96r
%8 [16r,32r:0) 0 at 16r  weight:INF
%15 [80r,80d:0) 0 at 80r  weight:INF
RegMasks:
********** MACHINEINSTRS **********
# Machine code for function scalar_mov_materializes_frame_index_unavailable_scc: NoPHIs, TracksLiveness, TiedOpsRewritten, TracksDebugUserValues
Frame Objects:
  fi#0: size=16384, align=64, at location [SP]
  fi#1: size=4, align=4, at location [SP]

0B	bb.0 (%ir-block.0):
16B	  %8:vgpr_32 = V_MOV_B32_e32 %stack.0.alloca0, implicit $exec
32B	  INLINEASM &"; use alloca0 $0" [sideeffect] [attdialect], $0:[reguse:VGPR_32], %8:vgpr_32
80B	  dead renamable $sgpr4_sgpr5 = S_AND_B64 0, $exec, implicit-def $scc
96B	  $sgpr59 = S_MOV_B32 %stack.1.alloca1
112B	  INLINEASM &"; use $0, $1" [sideeffect] [attdialect], $0:[reguse], $sgpr59, $1:[reguse], killed $scc
128B	  SI_RETURN

# End machine code for function scalar_mov_materializes_frame_index_unavailable_scc.

*** Bad machine code: No live segment at use ***
- function:    scalar_mov_materializes_frame_index_unavailable_scc
- basic block: %bb.0  (0x55ed7ac21b50) [0B;144B)
- instruction: 112B	INLINEASM &"; use $0, $1" [sideeffect] [attdialect], $0:[reguse], $sgpr59, $1:[reguse], killed $scc
- operand 3:   $sgpr59
- liverange:   [96r,96d:0) 0 at 96r
- regunit:     SGPR59_LO16
- at:          112B

*** Bad machine code: No live segment at use ***
- function:    scalar_mov_materializes_frame_index_unavailable_scc
- basic block: %bb.0  (0x55ed7ac21b50) [0B;144B)
- instruction: 112B	INLINEASM &"; use $0, $1" [sideeffect] [attdialect], $0:[reguse], $sgpr59, $1:[reguse], killed $scc
- operand 3:   $sgpr59
- liverange:   [96r,96d:0) 0 at 96r
- regunit:     SGPR59_HI16
- at:          112B
LLVM ERROR: Found 2 machine code errors.
```
(also seen if you compile with EXPENSIVE_CHECKS and run lit tests, as the failed build bot shows)

https://github.com/llvm/llvm-project/pull/127353