[llvm] [RegisterCoalescer] Deferring deletion of instructions in `ErasedInstrs` until the end of an iteration (PR #79820)

[Matt Arsenault via llvm-commits]

================
@@ -0,0 +1,213 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 4
+# RUN: llc -o - %s -mtriple=loongarch64 \
+# RUN:  -run-pass=register-coalescer -join-liveintervals=1 -join-splitedges=0 | FileCheck %s
+
+---
+name:            foo
+tracksRegLiveness: true
+body:             |
+  ; CHECK-LABEL: name: foo
+  ; CHECK: bb.0:
+  ; CHECK-NEXT:   successors: %bb.1(0x80000000)
+  ; CHECK-NEXT:   liveins: $r4, $r5, $r6, $r7, $r8
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gpr = COPY $r8
+  ; CHECK-NEXT:   [[COPY1:%[0-9]+]]:gpr = COPY $r7
+  ; CHECK-NEXT:   [[COPY2:%[0-9]+]]:gpr = COPY $r6
+  ; CHECK-NEXT:   [[COPY3:%[0-9]+]]:gpr = COPY $r5
+  ; CHECK-NEXT:   [[COPY4:%[0-9]+]]:gpr = COPY $r4
+  ; CHECK-NEXT:   [[ANDI:%[0-9]+]]:gpr = ANDI [[COPY3]], 1
+  ; CHECK-NEXT:   [[ORI:%[0-9]+]]:gpr = ORI $r0, 1
+  ; CHECK-NEXT:   [[ANDI1:%[0-9]+]]:gpr = ANDI [[COPY2]], 1
+  ; CHECK-NEXT:   [[ANDI2:%[0-9]+]]:gpr = ANDI [[COPY1]], 1
+  ; CHECK-NEXT:   [[ANDI3:%[0-9]+]]:gpr = ANDI [[COPY]], 1
+  ; CHECK-NEXT:   [[COPY5:%[0-9]+]]:gpr = COPY $r0
+  ; CHECK-NEXT:   [[COPY6:%[0-9]+]]:gpr = COPY $r0
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1:
+  ; CHECK-NEXT:   successors: %bb.2(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY7:%[0-9]+]]:gpr = COPY [[COPY5]]
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.2:
+  ; CHECK-NEXT:   successors: %bb.3(0x40000000), %bb.4(0x40000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   BEQZ [[ANDI]], %bb.4
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.3:
+  ; CHECK-NEXT:   successors: %bb.9(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   PseudoBR %bb.9
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.4:
+  ; CHECK-NEXT:   successors: %bb.5(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.5:
+  ; CHECK-NEXT:   successors: %bb.7(0x7c000000), %bb.6(0x04000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   dead [[LD_D:%[0-9]+]]:gpr = LD_D $r0, 8
+  ; CHECK-NEXT:   dead [[LD_D1:%[0-9]+]]:gpr = LD_D $r0, 0
+  ; CHECK-NEXT:   BNEZ [[ANDI1]], %bb.7
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.6:
+  ; CHECK-NEXT:   successors: %bb.11(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY6:%[0-9]+]]:gpr = COPY $r0
+  ; CHECK-NEXT:   PseudoBR %bb.11
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.7:
+  ; CHECK-NEXT:   successors: %bb.8(0x7c000000), %bb.10(0x04000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   BEQZ [[ANDI2]], %bb.10
+  ; CHECK-NEXT:   PseudoBR %bb.8
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.8:
+  ; CHECK-NEXT:   successors: %bb.9(0x04000000), %bb.5(0x7c000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY6:%[0-9]+]]:gpr = ADDI_D [[COPY6]], 1
+  ; CHECK-NEXT:   BEQZ [[ANDI3]], %bb.5
+  ; CHECK-NEXT:   PseudoBR %bb.9
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.9:
+  ; CHECK-NEXT:   successors: %bb.12(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   ST_B $r0, [[COPY4]], 0
+  ; CHECK-NEXT:   PseudoBR %bb.12
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.10:
+  ; CHECK-NEXT:   successors: %bb.11(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY5:%[0-9]+]]:gpr = ADDI_D [[COPY6]], 1
+  ; CHECK-NEXT:   [[COPY6:%[0-9]+]]:gpr = COPY [[ORI]]
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.11:
+  ; CHECK-NEXT:   successors: %bb.12(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   ST_D $r0, [[COPY4]], 0
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.12:
+  ; CHECK-NEXT:   successors: %bb.2(0x7c000000), %bb.1(0x04000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   BEQ [[COPY7]], [[ORI]], %bb.2
+  ; CHECK-NEXT:   PseudoBR %bb.1
+  bb.0:
+    liveins: $r4, $r5, $r6, $r7, $r8
+
+    %22:gpr = COPY killed $r8
+    %21:gpr = COPY killed $r7
----------------
arsenm wrote:

run-pass=none will still compact these numbers (which makes it easier to read 1:1 correspondence to the debug output)

https://github.com/llvm/llvm-project/pull/79820