[llvm] [RISCV] Fix crash when trying to remove segment (PR #146524)

[Luke Lau via llvm-commits]

================
@@ -622,3 +640,75 @@ body: |
     dead $x0 = PseudoVSETIVLI 1, 208, implicit-def $vl, implicit-def $vtype
     %v:vr = COPY $v8, implicit $vtype
     %x = PseudoVSETVLI %x, 208, implicit-def $vl, implicit-def $vtype
+...
+---
+name:            vsetvli_vleff
+alignment:       4
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: gpr, preferred-register: '' }
+  - { id: 1, class: gpr, preferred-register: '' }
+  - { id: 2, class: gpr, preferred-register: '' }
+  - { id: 3, class: gpr, preferred-register: '' }
+  - { id: 4, class: gpr, preferred-register: '' }
+  - { id: 5, class: vr, preferred-register: '%7' }
+  - { id: 6, class: gpr, preferred-register: '' }
+  - { id: 7, class: vr, preferred-register: '%5' }
+  - { id: 8, class: vr, preferred-register: '' }
+  - { id: 9, class: gpr, preferred-register: '' }
+frameInfo:
+  maxAlignment:    1
+machineFunctionInfo: {}
+body:             |
+  ; CHECK-LABEL: name: vsetvli_vleff
+  ; CHECK: bb.0.entry:
+  ; CHECK-NEXT:   successors: %bb.1(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gpr = COPY $x0
+  ; CHECK-NEXT:   dead [[PseudoVSETVLIX0_:%[0-9]+]]:gprnox0 = PseudoVSETVLIX0 killed $x0, 200 /* e16, m1, ta, ma */, implicit-def $vl, implicit-def $vtype
+  ; CHECK-NEXT:   renamable $v8 = PseudoVMV_V_I_M1 undef renamable $v8, 0, -1, 4 /* e16 */, 0 /* tu, mu */, implicit $vl, implicit $vtype
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1.while.cond:
+  ; CHECK-NEXT:   successors: %bb.2(0x7c000000), %bb.3(0x04000000)
+  ; CHECK-NEXT:   liveins: $v8
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   BNE [[COPY]], $x0, %bb.3
+  ; CHECK-NEXT:   PseudoBR %bb.2
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.2.while.body:
+  ; CHECK-NEXT:   successors: %bb.1(0x80000000)
+  ; CHECK-NEXT:   liveins: $v8
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   $x0 = PseudoVSETIVLI 0, 136 /* e16, m1, tu, ma */, implicit-def $vl, implicit-def $vtype
+  ; CHECK-NEXT:   renamable $v9 = COPY renamable $v8, implicit $vtype
+  ; CHECK-NEXT:   dead renamable $v9, $x0 = PseudoVLE16FF_V_M1 killed renamable $v9, $x0, 0, 4 /* e16 */, 2 /* tu, ma */, implicit-def dead $vl, implicit $vl, implicit $vtype :: (load unknown-size from `ptr null`, align 2)
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gpr = PseudoReadVL implicit $vl
+  ; CHECK-NEXT:   PseudoBR %bb.1
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.3.while.end:
+  ; CHECK-NEXT:   $x10 = COPY $x0
+  ; CHECK-NEXT:   PseudoRET implicit killed $x10
+  bb.0.entry:
+    successors: %bb.1(0x80000000)
+
+    %9:gpr = COPY $x0
+    renamable $v8 = PseudoVMV_V_I_M1 undef renamable $v8, 0, -1, 4 /* e16 */, 0 /* tu, mu */
+
+  bb.1.while.cond:
+    successors: %bb.2(0x7c000000), %bb.3(0x04000000)
+    liveins: $v8
+
+    BNE %9, $x0, %bb.3
+    PseudoBR %bb.2
+
+  bb.2.while.body:
+    successors: %bb.1(0x80000000)
+    liveins: $v8
+
+    renamable $v9 = COPY renamable $v8
+    dead renamable $v9, %9:gpr = PseudoVLE16FF_V_M1 killed renamable $v9, $x0, 0, 4 /* e16 */, 2 /* tu, ma */, implicit-def dead $vl :: (load unknown-size from `ptr null`, align 2)
+    PseudoBR %bb.1
+
+  bb.3.while.end:
+    $x10 = COPY $x0
+    PseudoRET implicit killed $x10
----------------
lukel97 wrote:

I think this can be made more minimal, something like this should reproduce the crash?

```yaml
---
name: vsetvli_vleff
tracksRegLiveness: true
body: |
  bb.0:
    PseudoBR %bb.2
  bb.1:
    $x8 = COPY %vl
    PseudoRET implicit $x8
  bb.2:
    $noreg, %vl:gpr = PseudoVLE16FF_V_M1 $noreg, $noreg, 0, 4 /* e16 */, 2 /* tu, ma */
    PseudoBR %bb.1
```

https://github.com/llvm/llvm-project/pull/146524