Index: llvm/include/llvm/CodeGen/GlobalISel/LegalizerInfo.h
===================================================================
--- llvm/include/llvm/CodeGen/GlobalISel/LegalizerInfo.h
+++ llvm/include/llvm/CodeGen/GlobalISel/LegalizerInfo.h
@@ -661,6 +661,7 @@
 
   /// The instruction is unsupported.
   LegalizeRuleSet &unsupported() {
+    markAllIdxsAsCovered();
     return actionIf(LegalizeAction::Unsupported, always);
   }
   LegalizeRuleSet &unsupportedIf(LegalityPredicate Predicate) {
Index: llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp
+++ llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp
@@ -1101,6 +1101,11 @@
 
   getActionDefinitionsBuilder(G_SEXT_INREG).lower();
 
+  getActionDefinitionsBuilder({G_VASTART, G_VAARG, G_BRJT, G_JUMP_TABLE,
+        G_DYN_STACKALLOC, G_INDEXED_LOAD, G_INDEXED_SEXTLOAD,
+        G_INDEXED_ZEXTLOAD, G_INDEXED_STORE})
+    .unsupported();
+
   computeTables();
   verify(*ST.getInstrInfo());
 }
Index: llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-jump-table.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-jump-table.mir
@@ -0,0 +1,78 @@
+# RUN: not llc -march=amdgcn -run-pass=legalizer -o /dev/null %s 2>&1  | FileCheck %s
+
+# CHECK: LLVM ERROR: unable to legalize instruction: %3:_(p0) = G_JUMP_TABLE %jump-table.0 (in function: jt_test)
+
+# FIXME: This could probably be smaller, but the jump table MIR parsing is very crashy.
+
+--- |
+  define i32 @jt_test(i32 %x) {
+  entry:
+    switch i32 %x, label %return [
+      i32 75, label %sw.bb
+      i32 34, label %sw.bb
+      i32 56, label %sw.bb
+      i32 35, label %sw.bb
+      i32 40, label %sw.bb
+      i32 4, label %sw.bb1
+      i32 5, label %sw.bb1
+      i32 6, label %sw.bb1
+    ]
+
+  sw.bb:                                            ; preds = %entry, %entry, %entry, %entry, %entry
+    %add = add nsw i32 %x, 42
+    br label %return
+
+  sw.bb1:                                           ; preds = %entry, %entry, %entry
+    %mul = mul nsw i32 %x, 3
+    br label %return
+
+  return:                                           ; preds = %sw.bb1, %sw.bb, %entry
+    %retval.0 = phi i32 [ %mul, %sw.bb1 ], [ %add, %sw.bb ], [ 0, %entry ]
+    ret i32 %retval.0
+  }
+
+...
+---
+name:            jt_test
+tracksRegLiveness: true
+jumpTable:
+  kind:            block-address
+  entries:
+    - id:              0
+      blocks:          [ '%bb.3', '%bb.3', '%bb.3', '%bb.4', '%bb.4', '%bb.4',
+                         '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4',
+                         '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4',
+                         '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4',
+                         '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4',
+                         '%bb.2', '%bb.2', '%bb.4', '%bb.4', '%bb.4', '%bb.4',
+                         '%bb.2', '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4',
+                         '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4',
+                         '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.2', '%bb.4',
+                         '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4',
+                         '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4',
+                         '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.4', '%bb.2' ]
+body:             |
+  bb.0.entry:
+    liveins: $sgpr0
+
+    %0:_(s32) = COPY $sgpr0
+    %1:_(s32) = G_CONSTANT i32 0
+    %2:_(s1) = G_ICMP intpred(ugt), %0, %1
+    %3:_(p0) = G_JUMP_TABLE %jump-table.0
+    S_NOP 0, implicit %3
+    G_BRCOND %2, %bb.4
+
+  bb.1.entry:
+    successors: %bb.3(0x2aaaaaab), %bb.4(0x2aaaaaab), %bb.2(0x2aaaaaab)
+
+    G_BR %bb.4
+
+  bb.2.sw.bb:
+    G_BR %bb.4
+
+  bb.3.sw.bb1:
+
+  bb.4.return:
+    S_ENDPGM 0
+
+...