--- /dev/null
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -march=amdgcn -verify-machineinstrs -run-pass=simple-register-coalescing -o - %s | FileCheck %s
+
+# Test used to crash with message:
+# JoinVals::computeAssignment(unsigned int, (anonymous namespace)::JoinVals &): Assertion `Assignments[ValNo] != -1 && "Bad recursion?"' failed.
+
+# The issue was with processing two operands are parts of the same reg and are
+# used in the same instruction (e.g. inline asm): first is "def early-clobber",
+# while the other is just "def".
+# Register coalescer ran in bad recursion if the early clobbered subreg is
+# second in the following sequence of COPYs.
+
+---
+name: foo1
+tracksRegLiveness: true
+body: |
+ bb.0:
+ liveins: $vgpr0_vgpr1
+
+ ; CHECK-LABEL: name: foo1
+ ; CHECK: liveins: $vgpr0_vgpr1
+ ; CHECK-NEXT: {{ $}}
+ ; CHECK-NEXT: INLINEASM &"", 0 /* attdialect */, 1835018 /* regdef:VGPR_32 */, def undef %2.sub0, 1835019 /* regdef-ec:VGPR_32 */, def undef early-clobber %2.sub1
+ ; CHECK-NEXT: FLAT_STORE_DWORDX2 $vgpr0_vgpr1, %2, 0, 0, implicit $exec, implicit $flat_scr :: (store (s64))
+ ; CHECK-NEXT: S_ENDPGM 0
+ INLINEASM &"", 0 /* attdialect */, 1835018 /* regdef:VGPR_32 */, def %0:vgpr_32, 1835019 /* regdef-ec:VGPR_32 */, def early-clobber %1:vgpr_32
+ undef %2.sub0:vreg_64 = COPY killed %0
+ %2.sub1:vreg_64 = COPY killed %1
+ FLAT_STORE_DWORDX2 killed $vgpr0_vgpr1, killed %2, 0, 0, implicit $exec, implicit $flat_scr :: (store (s64))
+ S_ENDPGM 0
+
+...
+
+---
+name: foo2
+tracksRegLiveness: true
+body: |
+ bb.0:
+ liveins: $vgpr0_vgpr1
+
+ ; CHECK-LABEL: name: foo2
+ ; CHECK: liveins: $vgpr0_vgpr1
+ ; CHECK-NEXT: {{ $}}
+ ; CHECK-NEXT: INLINEASM &"", 0 /* attdialect */, 1835019 /* regdef-ec:VGPR_32 */, def undef early-clobber %2.sub1, 1835018 /* regdef:VGPR_32 */, def undef %2.sub0
+ ; CHECK-NEXT: FLAT_STORE_DWORDX2 $vgpr0_vgpr1, %2, 0, 0, implicit $exec, implicit $flat_scr :: (store (s64))
+ ; CHECK-NEXT: S_ENDPGM 0
+ INLINEASM &"", 0 /* attdialect */, 1835019 /* regdef-ec:VGPR_32 */, def early-clobber %1:vgpr_32, 1835018 /* regdef:VGPR_32 */, def %0:vgpr_32
+ undef %2.sub0:vreg_64 = COPY killed %0
+ %2.sub1:vreg_64 = COPY killed %1
+ FLAT_STORE_DWORDX2 killed $vgpr0_vgpr1, killed %2, 0, 0, implicit $exec, implicit $flat_scr :: (store (s64))
+ S_ENDPGM 0
+
+...
+
+---
+name: foo3
+tracksRegLiveness: true
+body: |
+ bb.0:
+ liveins: $vgpr0_vgpr1
+
+ ; CHECK-LABEL: name: foo3
+ ; CHECK: liveins: $vgpr0_vgpr1
+ ; CHECK-NEXT: {{ $}}
+ ; CHECK-NEXT: INLINEASM &"", 0 /* attdialect */, 1835018 /* regdef:VGPR_32 */, def undef %2.sub0, 1835019 /* regdef-ec:VGPR_32 */, def undef early-clobber %2.sub1
+ ; CHECK-NEXT: FLAT_STORE_DWORDX2 $vgpr0_vgpr1, %2, 0, 0, implicit $exec, implicit $flat_scr :: (store (s64))
+ ; CHECK-NEXT: S_ENDPGM 0
+ INLINEASM &"", 0 /* attdialect */, 1835018 /* regdef:VGPR_32 */, def %1:vgpr_32, 1835019 /* regdef-ec:VGPR_32 */, def early-clobber %0:vgpr_32
+ undef %2.sub0:vreg_64 = COPY killed %1
+ %2.sub1:vreg_64 = COPY killed %0
+ FLAT_STORE_DWORDX2 killed $vgpr0_vgpr1, killed %2, 0, 0, implicit $exec, implicit $flat_scr :: (store (s64))
+ S_ENDPGM 0
+
+...
+
+---
+name: foo4
+tracksRegLiveness: true
+body: |
+ bb.0:
+ liveins: $vgpr0_vgpr1
+
+ ; CHECK-LABEL: name: foo4
+ ; CHECK: liveins: $vgpr0_vgpr1
+ ; CHECK-NEXT: {{ $}}
+ ; CHECK-NEXT: INLINEASM &"", 0 /* attdialect */, 1835019 /* regdef-ec:VGPR_32 */, def undef early-clobber %2.sub1, 1835018 /* regdef:VGPR_32 */, def undef %2.sub0
+ ; CHECK-NEXT: FLAT_STORE_DWORDX2 $vgpr0_vgpr1, %2, 0, 0, implicit $exec, implicit $flat_scr :: (store (s64))
+ ; CHECK-NEXT: S_ENDPGM 0
+ INLINEASM &"", 0 /* attdialect */, 1835019 /* regdef-ec:VGPR_32 */, def early-clobber %0:vgpr_32, 1835018 /* regdef:VGPR_32 */, def %1:vgpr_32
+ undef %2.sub0:vreg_64 = COPY killed %1
+ %2.sub1:vreg_64 = COPY killed %0
+ FLAT_STORE_DWORDX2 killed $vgpr0_vgpr1, killed %2, 0, 0, implicit $exec, implicit $flat_scr :: (store (s64))
+ S_ENDPGM 0
+
+...