Index: lib/Target/AMDGPU/SIInstrInfo.cpp
===================================================================
--- lib/Target/AMDGPU/SIInstrInfo.cpp
+++ lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -2514,6 +2514,10 @@
     return MI.readsRegister(AMDGPU::EXEC, &RI);
   }
 
+  // Make a conservative assumption about the callee.
+  if (MI.isCall())
+    return true;
+
   // Be conservative with any unhandled generic opcodes.
   if (!isTargetSpecificOpcode(MI.getOpcode()))
     return true;
Index: test/CodeGen/AMDGPU/collapse-endcf2.mir
===================================================================
--- /dev/null
+++ test/CodeGen/AMDGPU/collapse-endcf2.mir
@@ -0,0 +1,121 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -march=amdgcn -verify-machineinstrs -run-pass=si-optimize-exec-masking-pre-ra %s -o - | FileCheck -check-prefix=GCN %s
+
+--- |
+  define amdgpu_kernel void @call_no_explicit_exec_dependency () {
+    unreachable
+  }
+
+  declare void @func()
+
+...
+
+# Call should be assumed to read exec
+---
+name: call_no_explicit_exec_dependency
+tracksRegLiveness: true
+liveins:
+  - { reg: '$vgpr0', virtual-reg: '%0' }
+  - { reg: '$sgpr0_sgpr1', virtual-reg: '%1' }
+machineFunctionInfo:
+  isEntryFunction: true
+body:             |
+  ; GCN-LABEL: name: call_no_explicit_exec_dependency
+  ; GCN: bb.0:
+  ; GCN:   successors: %bb.1(0x40000000), %bb.4(0x40000000)
+  ; GCN:   liveins: $vgpr0, $sgpr0_sgpr1
+  ; GCN:   [[COPY:%[0-9]+]]:sgpr_64 = COPY $sgpr0_sgpr1
+  ; GCN:   [[COPY1:%[0-9]+]]:vgpr_32 = COPY $vgpr0
+  ; GCN:   [[V_CMP_LT_U32_e64_:%[0-9]+]]:sreg_64 = V_CMP_LT_U32_e64 1, [[COPY1]], implicit $exec
+  ; GCN:   [[COPY2:%[0-9]+]]:sreg_64 = COPY $exec, implicit-def $exec
+  ; GCN:   [[S_AND_B64_:%[0-9]+]]:sreg_64 = S_AND_B64 [[COPY2]], [[V_CMP_LT_U32_e64_]], implicit-def dead $scc
+  ; GCN:   $exec = S_MOV_B64_term [[S_AND_B64_]]
+  ; GCN:   SI_MASK_BRANCH %bb.4, implicit $exec
+  ; GCN:   S_BRANCH %bb.1
+  ; GCN: bb.1:
+  ; GCN:   successors: %bb.2(0x40000000), %bb.3(0x40000000)
+  ; GCN:   undef %5.sub0_sub1:sgpr_128 = S_LOAD_DWORDX2_IMM [[COPY]], 9, 0, 0 :: (dereferenceable invariant load 8, align 4, addrspace 4)
+  ; GCN:   undef %6.sub0:vreg_64 = V_LSHLREV_B32_e32 2, [[COPY1]], implicit $exec
+  ; GCN:   %6.sub1:vreg_64 = V_MOV_B32_e32 0, implicit $exec
+  ; GCN:   [[COPY3:%[0-9]+]]:vgpr_32 = COPY %5.sub1
+  ; GCN:   undef %8.sub0:vreg_64, %9:sreg_64_xexec = V_ADD_I32_e64 %5.sub0, %6.sub0, 0, implicit $exec
+  ; GCN:   %8.sub1:vreg_64, dead %10:sreg_64_xexec = V_ADDC_U32_e64 0, [[COPY3]], %9, 0, implicit $exec
+  ; GCN:   %5.sub3:sgpr_128 = S_MOV_B32 61440
+  ; GCN:   %5.sub2:sgpr_128 = S_MOV_B32 0
+  ; GCN:   BUFFER_STORE_DWORD_ADDR64 %6.sub1, %6, %5, 0, 0, 0, 0, 0, 0, implicit $exec :: (store 4, addrspace 1)
+  ; GCN:   [[V_CMP_NE_U32_e64_:%[0-9]+]]:sreg_64 = V_CMP_NE_U32_e64 2, [[COPY1]], implicit $exec
+  ; GCN:   [[COPY4:%[0-9]+]]:sreg_64 = COPY $exec, implicit-def $exec
+  ; GCN:   [[S_AND_B64_1:%[0-9]+]]:sreg_64 = S_AND_B64 [[COPY4]], [[V_CMP_NE_U32_e64_]], implicit-def dead $scc
+  ; GCN:   $exec = S_MOV_B64_term [[S_AND_B64_1]]
+  ; GCN:   SI_MASK_BRANCH %bb.3, implicit $exec
+  ; GCN:   S_BRANCH %bb.2
+  ; GCN: bb.2:
+  ; GCN:   successors: %bb.3(0x80000000)
+  ; GCN:   %5.sub0:sgpr_128 = COPY %5.sub2
+  ; GCN:   %5.sub1:sgpr_128 = COPY %5.sub2
+  ; GCN:   [[V_MOV_B32_e32_:%[0-9]+]]:vgpr_32 = V_MOV_B32_e32 1, implicit $exec
+  ; GCN:   BUFFER_STORE_DWORD_ADDR64 [[V_MOV_B32_e32_]], %8, %5, 0, 4, 0, 0, 0, 0, implicit $exec :: (store 4, addrspace 1)
+  ; GCN: bb.3:
+  ; GCN:   successors: %bb.4(0x80000000)
+  ; GCN:   $exec = S_OR_B64 $exec, [[COPY4]], implicit-def $scc
+  ; GCN:   [[DEF:%[0-9]+]]:sreg_64 = IMPLICIT_DEF
+  ; GCN:   dead %16:sreg_64 = SI_CALL [[DEF]], @func, csr_amdgpu_highregs
+  ; GCN: bb.4:
+  ; GCN:   $exec = S_OR_B64 $exec, [[COPY2]], implicit-def $scc
+  ; GCN:   [[V_MOV_B32_e32_1:%[0-9]+]]:vgpr_32 = V_MOV_B32_e32 3, implicit $exec
+  ; GCN:   [[V_MOV_B32_e32_2:%[0-9]+]]:vgpr_32 = V_MOV_B32_e32 0, implicit $exec
+  ; GCN:   $m0 = S_MOV_B32 -1
+  ; GCN:   DS_WRITE_B32 [[V_MOV_B32_e32_2]], [[V_MOV_B32_e32_1]], 0, 0, implicit $m0, implicit $exec :: (store 4, addrspace 3)
+  ; GCN:   S_ENDPGM 0
+  bb.0:
+    successors: %bb.1, %bb.4
+    liveins: $vgpr0, $sgpr0_sgpr1
+
+    %1:sgpr_64 = COPY $sgpr0_sgpr1
+    %0:vgpr_32 = COPY $vgpr0
+    %2:sreg_64 = V_CMP_LT_U32_e64 1, %0, implicit $exec
+    %3:sreg_64 = COPY $exec, implicit-def $exec
+    %4:sreg_64 = S_AND_B64 %3, %2, implicit-def dead $scc
+    $exec = S_MOV_B64_term %4
+    SI_MASK_BRANCH %bb.4, implicit $exec
+    S_BRANCH %bb.1
+
+  bb.1:
+    successors: %bb.2, %bb.3
+
+    undef %5.sub0_sub1:sgpr_128 = S_LOAD_DWORDX2_IMM %1, 9, 0, 0 :: (dereferenceable invariant load 8, align 4, addrspace 4)
+    undef %6.sub0:vreg_64 = V_LSHLREV_B32_e32 2, %0, implicit $exec
+    %6.sub1:vreg_64 = V_MOV_B32_e32 0, implicit $exec
+    %7:vgpr_32 = COPY %5.sub1
+    undef %8.sub0:vreg_64, %9:sreg_64_xexec = V_ADD_I32_e64 %5.sub0, %6.sub0, 0, implicit $exec
+    %8.sub1:vreg_64, dead %10:sreg_64_xexec = V_ADDC_U32_e64 0, %7, %9, 0, implicit $exec
+    %5.sub3:sgpr_128 = S_MOV_B32 61440
+    %5.sub2:sgpr_128 = S_MOV_B32 0
+    BUFFER_STORE_DWORD_ADDR64 %6.sub1, %6, %5, 0, 0, 0, 0, 0, 0, implicit $exec :: (store 4, addrspace 1)
+    %11:sreg_64 = V_CMP_NE_U32_e64 2, %0, implicit $exec
+    %12:sreg_64 = COPY $exec, implicit-def $exec
+    %13:sreg_64 = S_AND_B64 %12, %11, implicit-def dead $scc
+    $exec = S_MOV_B64_term %13
+    SI_MASK_BRANCH %bb.3, implicit $exec
+    S_BRANCH %bb.2
+
+  bb.2:
+    %5.sub0:sgpr_128 = COPY %5.sub2
+    %5.sub1:sgpr_128 = COPY %5.sub2
+    %14:vgpr_32 = V_MOV_B32_e32 1, implicit $exec
+    BUFFER_STORE_DWORD_ADDR64 %14, %8, %5, 0, 4, 0, 0, 0, 0, implicit $exec :: (store 4, addrspace 1)
+
+  bb.3:
+    $exec = S_OR_B64 $exec, %12,  implicit-def $scc
+    %20:sreg_64 = IMPLICIT_DEF
+    %21:sreg_64 = SI_CALL %20, @func, csr_amdgpu_highregs
+
+  bb.4:
+    $exec = S_OR_B64 $exec, %3, implicit-def $scc
+    %17:vgpr_32 = V_MOV_B32_e32 3, implicit $exec
+    %18:vgpr_32 = V_MOV_B32_e32 0, implicit $exec
+    $m0 = S_MOV_B32 -1
+    DS_WRITE_B32 %18, %17, 0, 0, implicit $m0, implicit $exec :: (store 4, addrspace 3)
+    S_ENDPGM 0
+
+...