Index: lib/Target/AMDGPU/SIInstrInfo.h
===================================================================
--- lib/Target/AMDGPU/SIInstrInfo.h
+++ lib/Target/AMDGPU/SIInstrInfo.h
@@ -624,6 +624,10 @@
   /// Whether we must prevent this instruction from executing with EXEC = 0.
   bool hasUnwantedEffectsWhenEXECEmpty(const MachineInstr &MI) const;
 
+  /// Returns true if the instruction could potentially depend on the value of
+  /// exec. If false, exec dependencies may safely be ignored.
+  bool mayReadEXEC(const MachineRegisterInfo &MRI, const MachineInstr &MI) const;
+
   bool isInlineConstant(const APInt &Imm) const;
 
   bool isInlineConstant(const MachineOperand &MO, uint8_t OperandType) const;
Index: lib/Target/AMDGPU/SIInstrInfo.cpp
===================================================================
--- lib/Target/AMDGPU/SIInstrInfo.cpp
+++ lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -2446,6 +2446,27 @@
   return false;
 }
 
+bool SIInstrInfo::mayReadEXEC(const MachineRegisterInfo &MRI,
+                              const MachineInstr &MI) const {
+  if (MI.isMetaInstruction())
+    return false;
+
+  // This won't read exec if this is an SGPR->SGPR copy.
+  if (MI.isCopyLike()) {
+    if (!RI.isSGPRReg(MRI, MI.getOperand(0).getReg()))
+      return true;
+
+    // Make sure this isn't copying exec as a normal operand
+    return MI.readsRegister(AMDGPU::EXEC, &RI);
+  }
+
+  // Be conservative with any unhandled generic opcodes.
+  if (!isTargetSpecificOpcode(MI.getOpcode()))
+    return true;
+
+  return !isSALU(MI) || MI.readsRegister(AMDGPU::EXEC, &RI);
+}
+
 bool SIInstrInfo::isInlineConstant(const APInt &Imm) const {
   switch (Imm.getBitWidth()) {
   case 32:
Index: lib/Target/AMDGPU/SIOptimizeExecMaskingPreRA.cpp
===================================================================
--- lib/Target/AMDGPU/SIOptimizeExecMaskingPreRA.cpp
+++ lib/Target/AMDGPU/SIOptimizeExecMaskingPreRA.cpp
@@ -33,10 +33,22 @@
 namespace {
 
 class SIOptimizeExecMaskingPreRA : public MachineFunctionPass {
+private:
+  const SIRegisterInfo *TRI;
+  const SIInstrInfo *TII;
+  MachineRegisterInfo *MRI;
+
 public:
-  static char ID;
+  MachineBasicBlock::iterator skipIgnoreExecInsts(
+    MachineBasicBlock::iterator I, MachineBasicBlock::iterator E) const;
+
+    MachineBasicBlock::iterator skipIgnoreExecInstsTrivialSucc(
+      MachineBasicBlock *&MBB,
+      MachineBasicBlock::iterator It) const;
 
 public:
+  static char ID;
+
   SIOptimizeExecMaskingPreRA() : MachineFunctionPass(ID) {
     initializeSIOptimizeExecMaskingPreRAPass(*PassRegistry::getPassRegistry());
   }
@@ -102,6 +114,45 @@
   return SaveExecInst;
 }
 
+/// Skip over instructions that don't care about the exec mask.
+MachineBasicBlock::iterator SIOptimizeExecMaskingPreRA::skipIgnoreExecInsts(
+  MachineBasicBlock::iterator I, MachineBasicBlock::iterator E) const {
+  for ( ; I != E; ++I) {
+    if (TII->mayReadEXEC(*MRI, *I))
+      break;
+  }
+
+  return I;
+}
+
+// Skip to the next instruction, ignoring debug instructions, and trivial block
+// boundaries (blocks that have one (typically fallthrough) successor, and the
+// successor has one predecessor.
+MachineBasicBlock::iterator
+SIOptimizeExecMaskingPreRA::skipIgnoreExecInstsTrivialSucc(
+  MachineBasicBlock *&MBB,
+  MachineBasicBlock::iterator It) const {
+
+  do {
+    It = skipIgnoreExecInsts(It, MBB->end());
+    if (It != MBB->end() || MBB->succ_size() != 1)
+      break;
+
+    // If there is one trivial successor, advance to the next block.
+    MachineBasicBlock *Succ = *MBB->succ_begin();
+
+    // TODO: Is this really necessary?
+    if (!MBB->isLayoutSuccessor(Succ))
+      break;
+
+    It = Succ->begin();
+    MBB = Succ;
+  } while (true);
+
+  return It;
+}
+
+
 // Optimize sequence
 //    %sel = V_CNDMASK_B32_e64 0, 1, %cc
 //    %cmp = V_CMP_NE_U32 1, %1
@@ -227,8 +278,10 @@
     return false;
 
   const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
-  const SIRegisterInfo *TRI = ST.getRegisterInfo();
-  const SIInstrInfo *TII = ST.getInstrInfo();
+  TRI = ST.getRegisterInfo();
+  TII = ST.getInstrInfo();
+  MRI = &MF.getRegInfo();
+
   MachineRegisterInfo &MRI = MF.getRegInfo();
   LiveIntervals *LIS = &getAnalysis<LiveIntervals>();
   DenseSet<unsigned> RecalcRegs({AMDGPU::EXEC_LO, AMDGPU::EXEC_HI});
@@ -313,25 +366,9 @@
     if (MBB.succ_size() != 1 || Lead == E || !isEndCF(*Lead, TRI))
       continue;
 
-    const MachineBasicBlock* Succ = *MBB.succ_begin();
-    if (!MBB.isLayoutSuccessor(Succ))
-      continue;
-
-    auto I = std::next(Lead);
-
-    for ( ; I != E; ++I) {
-      if (I->isDebugInstr())
-        continue;
-
-      if (!TII->isSALU(*I) || I->readsRegister(AMDGPU::EXEC, TRI))
-        break;
-    }
-
-    if (I != E)
-      continue;
-
-    auto NextLead = skipDebugInstructionsForward(Succ->begin(), Succ->end());
-    if (NextLead == Succ->end() || !isEndCF(*NextLead, TRI) ||
+    MachineBasicBlock *TmpMBB = &MBB;
+    auto NextLead = skipIgnoreExecInstsTrivialSucc(TmpMBB, std::next(Lead));
+    if (NextLead == TmpMBB->end() || !isEndCF(*NextLead, TRI) ||
         !getOrExecSource(*NextLead, *TII, MRI))
       continue;
 
Index: test/CodeGen/AMDGPU/collapse-endcf.mir
===================================================================
--- test/CodeGen/AMDGPU/collapse-endcf.mir
+++ test/CodeGen/AMDGPU/collapse-endcf.mir
@@ -143,8 +143,7 @@
   ; GCN:   %5.sub2:sgpr_128 = S_MOV_B32 0
   ; GCN:   BUFFER_STORE_DWORD_ADDR64 %6.sub1, %6, %5, 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:   [[S_AND_B64_1:%[0-9]+]]:sreg_64 = S_AND_B64 $exec, [[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
@@ -156,7 +155,6 @@
   ; GCN:   BUFFER_STORE_DWORD_ADDR64 [[V_MOV_B32_e32_]], %8, %5, 0, 4, 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: bb.4:
   ; GCN:   successors: %bb.5(0x80000000)
   ; GCN: bb.5:
@@ -253,8 +251,7 @@
   ; GCN:   %5.sub2:sgpr_128 = S_MOV_B32 0
   ; GCN:   BUFFER_STORE_DWORD_ADDR64 %6.sub1, %6, %5, 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:   [[S_AND_B64_1:%[0-9]+]]:sreg_64 = S_AND_B64 $exec, [[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
@@ -266,7 +263,6 @@
   ; GCN:   BUFFER_STORE_DWORD_ADDR64 [[V_MOV_B32_e32_]], %8, %5, 0, 4, 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: bb.4:
   ; GCN:   successors: %bb.5(0x80000000)
   ; GCN:   DBG_VALUE
@@ -477,8 +473,7 @@
   ; GCN:   %5.sub2:sgpr_128 = S_MOV_B32 0
   ; GCN:   BUFFER_STORE_DWORD_ADDR64 %6.sub1, %6, %5, 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:   [[S_AND_B64_1:%[0-9]+]]:sreg_64 = S_AND_B64 $exec, [[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
@@ -490,7 +485,6 @@
   ; GCN:   BUFFER_STORE_DWORD_ADDR64 [[V_MOV_B32_e32_]], %8, %5, 0, 4, 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]+]]:sgpr_32 = IMPLICIT_DEF
   ; GCN:   [[S_BREV_B32_:%[0-9]+]]:sgpr_32 = S_BREV_B32 [[DEF]]
   ; GCN:   KILL [[DEF]]
@@ -773,3 +767,116 @@
 
 ...
 
+# There's no real reason this can't be handled, but isn't now.
+---
+name: simple_nested_if_not_layout_successor
+tracksRegLiveness: true
+liveins:
+  - { reg: '$vgpr0', virtual-reg: '%0' }
+  - { reg: '$sgpr0_sgpr1', virtual-reg: '%1' }
+machineFunctionInfo:
+  isEntryFunction: true
+body:             |
+  ; GCN-LABEL: name: simple_nested_if_not_layout_successor
+  ; 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 :: (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, 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, implicit $exec :: (store 4, addrspace 1)
+  ; GCN: bb.3:
+  ; GCN:   successors: %bb.5(0x80000000)
+  ; GCN:   $exec = S_OR_B64 $exec, [[COPY4]], implicit-def $scc
+  ; GCN:   S_BRANCH %bb.5
+  ; 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
+  ; GCN: bb.5:
+  ; GCN:   successors: %bb.4(0x80000000)
+  ; GCN:   S_BRANCH %bb.4
+  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 :: (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, 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, implicit $exec :: (store 4, addrspace 1)
+
+  bb.3:
+    $exec = S_OR_B64 $exec, %12, implicit-def $scc
+    S_BRANCH %bb.5
+
+  bb.4:
+    $exec = S_OR_B64 $exec, %3, implicit-def $scc
+    %15:vgpr_32 = V_MOV_B32_e32 3, implicit $exec
+    %16:vgpr_32 = V_MOV_B32_e32 0, implicit $exec
+    $m0 = S_MOV_B32 -1
+    DS_WRITE_B32 %16, %15, 0, 0, implicit $m0, implicit $exec :: (store 4, addrspace 3)
+    S_ENDPGM 0
+
+  bb.5:
+    S_BRANCH %bb.4
+
+...