Index: llvm/lib/CodeGen/RegAllocEvictionAdvisor.cpp
===================================================================
--- llvm/lib/CodeGen/RegAllocEvictionAdvisor.cpp
+++ llvm/lib/CodeGen/RegAllocEvictionAdvisor.cpp
@@ -236,7 +236,10 @@
                    MRI->getRegClass(Intf->reg())));
       // Only evict older cascades or live ranges without a cascade.
       unsigned IntfCascade = RA.getExtraInfo().getCascade(Intf->reg());
-      if (Cascade <= IntfCascade) {
+      if (Cascade == IntfCascade)
+        return false;
+
+      if (Cascade < IntfCascade) {
         if (!Urgent)
           return false;
         // We permit breaking cascades for urgent evictions. It should be the
Index: llvm/test/CodeGen/AMDGPU/illegal-eviction-assert.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AMDGPU/illegal-eviction-assert.mir
@@ -0,0 +1,37 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: not llc -march=amdgcn -mcpu=gfx900 -start-before=greedy,0 -stop-after=virtregrewriter,1 -o - 2>%t.err %s | FileCheck %s
+# RUN: FileCheck -check-prefix=ERR %s < %t.err
+
+# This testcase cannot be compiled. An attempted eviction legality
+# check was inconsistent with a later assertion when the eviction was
+# performed.
+
+# ERR: error: ran out of registers during register allocation
+
+--- |
+  define void @foo() #0 {
+    ret void
+  }
+
+  attributes #0 = { "amdgpu-waves-per-eu"="8,8"  }
+
+...
+
+# CHECK: S_NOP 0, implicit-def renamable $vgpr4_vgpr5_vgpr6_vgpr7_vgpr8_vgpr9_vgpr10_vgpr11_vgpr12_vgpr13_vgpr14_vgpr15_vgpr16_vgpr17_vgpr18_vgpr19, implicit-def renamable $vgpr20_vgpr21_vgpr22_vgpr23_vgpr24_vgpr25_vgpr26_vgpr27, implicit-def dead renamable $vgpr0_vgpr1_vgpr2_vgpr3, implicit-def renamable $vgpr28_vgpr29_vgpr30_vgpr31, implicit-def dead renamable $vgpr0_vgpr1_vgpr2_vgpr3
+# CHECK: S_NOP 0, implicit killed renamable $vgpr4_vgpr5_vgpr6_vgpr7_vgpr8_vgpr9_vgpr10_vgpr11_vgpr12_vgpr13_vgpr14_vgpr15_vgpr16_vgpr17_vgpr18_vgpr19, implicit killed renamable $vgpr20_vgpr21_vgpr22_vgpr23_vgpr24_vgpr25_vgpr26_vgpr27, implicit undef renamable $vgpr0_vgpr1_vgpr2_vgpr3, implicit killed renamable $vgpr28_vgpr29_vgpr30_vgpr31, implicit undef renamable $vgpr0_vgpr1_vgpr2_vgpr3
+
+---
+name:            foo
+tracksRegLiveness: true
+machineFunctionInfo:
+  scratchRSrcReg:  '$sgpr0_sgpr1_sgpr2_sgpr3'
+  frameOffsetReg:  '$sgpr33'
+  stackPtrOffsetReg: '$sgpr32'
+body:             |
+  bb.0:
+    S_NOP 0, implicit-def %0:vreg_512, implicit-def %1:vreg_256, implicit-def %2:vreg_128, implicit-def %3:vreg_128, implicit-def %4:vreg_128
+
+    S_NOP 0, implicit %0, implicit %1, implicit %2, implicit %3, implicit %4
+    S_ENDPGM 0
+
+...
Index: llvm/test/CodeGen/AMDGPU/regalloc-illegal-eviction-assert.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AMDGPU/regalloc-illegal-eviction-assert.ll
@@ -0,0 +1,29 @@
+; RUN: not llc -march=amdgcn -mcpu=gfx908 -verify-machineinstrs -o - %s 2>%t.err | FileCheck %s
+; RUN: FileCheck -check-prefix=ERR %s < %t.err
+
+; This testcase would fail on an "illegal eviction". If the assert was
+; relaxed to allow equivalent cascade numbers, it would infinite loop.
+
+; ERR: error: inline assembly requires more registers than available
+; ERR: error: inline assembly requires more registers than available
+
+%asm.output = type { <16 x i32>, <8 x i32>, <5 x i32>, <4 x i32>, <16 x i32> }
+
+; CHECK-LABEL: {{^}}illegal_eviction_assert:
+; CHECK: ; def v[4:19] v[20:27] v[0:4] v[0:3] a[0:15]
+; CHECK: ; clobber
+; CHECK: ; use v[4:19] v[20:27] v[0:4] v[0:3] a[1:16]
+define void @illegal_eviction_assert(<32 x i32> addrspace(1)* %arg) #0 {
+  ;%agpr0 = call i32 asm sideeffect "; def $0","=${a0}"()
+  %asm = call %asm.output asm sideeffect "; def $0 $1 $2 $3 $4","=v,=v,=v,=v,={a[0:15]}"()
+  %vgpr0 = extractvalue %asm.output %asm, 0
+  %vgpr1 = extractvalue %asm.output %asm, 1
+  %vgpr2 = extractvalue %asm.output %asm, 2
+  %vgpr3 = extractvalue %asm.output %asm, 3
+  %agpr0 = extractvalue %asm.output %asm, 4
+  call void asm sideeffect "; clobber", "~{v[0:31]}"()
+  call void asm sideeffect "; use $0 $1 $2 $3 $4","v,v,v,v,{a[1:16]}"(<16 x i32> %vgpr0, <8 x i32> %vgpr1, <5 x i32> %vgpr2, <4 x i32> %vgpr3, <16 x i32> %agpr0)
+  ret void
+}
+
+attributes #0 = { "amdgpu-waves-per-eu"="8,8" }