[CodeGen] Use first EHLabel as a stop gate for live range shrinking

This fixes issue #114194

The issue happens during the `LiveRangeShrink` pass, which runs early, before phi elimination.
LandingPads, which are lowered to EHLabels, need to be the first non phi instruction in an EHPad.
In case of a phi node being in front of the EHLabel and a use being after the EHLabel, we hoist the use in front of the label.

This results in a portion of the landingpad missing due to being hoisted in front of the label.

Author: MuellerMP

llvm/lib/CodeGen/LiveRangeShrink.cpp

@@ -74,16 +74,26 @@ using InstOrderMap = DenseMap<MachineInstr *, unsigned>;
 /// M[A] > M[B] guarantees that A is dominated by B.
 /// If \p New is not in \p M, return \p Old. Otherwise if \p Old is null, return
 /// \p New.
+/// If \p New is part of an EHPad and is not dominated by \p EHBarrier, return
+/// \p Old, because the start of the landingpad is required to be the first
+/// non-PHI instruction.
 static MachineInstr *FindDominatedInstruction(MachineInstr &New,
                                               MachineInstr *Old,
+                                              MachineInstr *EHBarrier,
                                               const InstOrderMap &M) {
   auto NewIter = M.find(&New);
   if (NewIter == M.end())
     return Old;
+  unsigned OrderNew = NewIter->second;
+  if (EHBarrier) {
+    unsigned OrderBarrier = M.find(EHBarrier)->second;
+    if (OrderBarrier > OrderNew) {
+      return Old;
+    }
+  }
   if (Old == nullptr)
     return &New;
   unsigned OrderOld = M.find(Old)->second;
-  unsigned OrderNew = NewIter->second;
   if (OrderOld != OrderNew)
     return OrderOld < OrderNew ? &New : Old;
   // OrderOld == OrderNew, we need to iterate down from Old to see if it
@@ -125,14 +135,19 @@ bool LiveRangeShrink::runOnMachineFunction(MachineFunction &MF) {
     if (MBB.empty())
       continue;
     bool SawStore = false;
+    bool IsEHPad = MBB.isEHPad();
+    MachineInstr *EHBarrier = nullptr;
     BuildInstOrderMap(MBB.begin(), IOM);
     UseMap.clear();
 
     for (MachineBasicBlock::iterator Next = MBB.begin(); Next != MBB.end();) {
       MachineInstr &MI = *Next;
       ++Next;
+
       if (MI.isPHI() || MI.isDebugOrPseudoInstr())
         continue;
+      if (IsEHPad && !EHBarrier && MI.isEHLabel())
+        EHBarrier = &MI;
       if (MI.mayStore())
         SawStore = true;
 
@@ -201,7 +216,7 @@ bool LiveRangeShrink::runOnMachineFunction(MachineFunction &MF) {
           MachineInstr &DefInstr = *MRI.def_instr_begin(Reg);
           if (!TII.isCopyInstr(DefInstr))
             NumEligibleUse++;
-          Insert = FindDominatedInstruction(DefInstr, Insert, IOM);
+          Insert = FindDominatedInstruction(DefInstr, Insert, EHBarrier, IOM);
         } else {
           Insert = nullptr;
           break;

llvm/test/CodeGen/X86/lrshrink-ehpad-phis.ll

@@ -0,0 +1,112 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc -mtriple x86_64-unknown-linux-gnu %s -o - | FileCheck %s
+
+declare i32 @__gxx_personality_v0(...)
+declare void @maythrow()
+declare void @cleanup(i32)
+
+@external_bool = external global i1
+@externalA = external global i32
+@externalB = external global i32
+@externalC = external global i32
+@externalD = external global i32
+
+define void @test() personality ptr @__gxx_personality_v0  {
+; CHECK-LABEL: test:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    pushq %rbp
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    pushq %r15
+; CHECK-NEXT:    .cfi_def_cfa_offset 24
+; CHECK-NEXT:    pushq %r14
+; CHECK-NEXT:    .cfi_def_cfa_offset 32
+; CHECK-NEXT:    pushq %r13
+; CHECK-NEXT:    .cfi_def_cfa_offset 40
+; CHECK-NEXT:    pushq %r12
+; CHECK-NEXT:    .cfi_def_cfa_offset 48
+; CHECK-NEXT:    pushq %rbx
+; CHECK-NEXT:    .cfi_def_cfa_offset 56
+; CHECK-NEXT:    pushq %rax
+; CHECK-NEXT:    .cfi_def_cfa_offset 64
+; CHECK-NEXT:    .cfi_offset %rbx, -56
+; CHECK-NEXT:    .cfi_offset %r12, -48
+; CHECK-NEXT:    .cfi_offset %r13, -40
+; CHECK-NEXT:    .cfi_offset %r14, -32
+; CHECK-NEXT:    .cfi_offset %r15, -24
+; CHECK-NEXT:    .cfi_offset %rbp, -16
+; CHECK-NEXT:    movq external_bool@GOTPCREL(%rip), %rax
+; CHECK-NEXT:    cmpb $1, (%rax)
+; CHECK-NEXT:    jne .LBB0_3
+; CHECK-NEXT:  # %bb.1: # %branchA
+; CHECK-NEXT:    movq externalA@GOTPCREL(%rip), %rax
+; CHECK-NEXT:    movl (%rax), %eax
+; CHECK-NEXT:    movl %eax, {{[-0-9]+}}(%r{{[sb]}}p) # 4-byte Spill
+; CHECK-NEXT:    movq externalC@GOTPCREL(%rip), %rax
+; CHECK-NEXT:    movl (%rax), %eax
+; CHECK-NEXT:    movl %eax, (%rsp) # 4-byte Spill
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:  .Ltmp2:
+; CHECK-NEXT:    callq maythrow@PLT
+; CHECK-NEXT:  .Ltmp3:
+; CHECK-NEXT:    jmp .LBB0_4
+; CHECK-NEXT:  .LBB0_3: # %branchB
+; CHECK-NEXT:    movq externalB@GOTPCREL(%rip), %rax
+; CHECK-NEXT:    movl (%rax), %eax
+; CHECK-NEXT:    movl %eax, {{[-0-9]+}}(%r{{[sb]}}p) # 4-byte Spill
+; CHECK-NEXT:    movq externalD@GOTPCREL(%rip), %rax
+; CHECK-NEXT:    movl (%rax), %eax
+; CHECK-NEXT:    movl %eax, (%rsp) # 4-byte Spill
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:  .Ltmp0:
+; CHECK-NEXT:    callq maythrow@PLT
+; CHECK-NEXT:  .Ltmp1:
+; CHECK-NEXT:  .LBB0_4: # %end
+; CHECK-NEXT:    addq $8, %rsp
+; CHECK-NEXT:    .cfi_def_cfa_offset 56
+; CHECK-NEXT:    popq %rbx
+; CHECK-NEXT:    .cfi_def_cfa_offset 48
+; CHECK-NEXT:    popq %r12
+; CHECK-NEXT:    .cfi_def_cfa_offset 40
+; CHECK-NEXT:    popq %r13
+; CHECK-NEXT:    .cfi_def_cfa_offset 32
+; CHECK-NEXT:    popq %r14
+; CHECK-NEXT:    .cfi_def_cfa_offset 24
+; CHECK-NEXT:    popq %r15
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    popq %rbp
+; CHECK-NEXT:    .cfi_def_cfa_offset 8
+; CHECK-NEXT:    retq
+; CHECK-NEXT:  .LBB0_2: # %lpad
+; CHECK-NEXT:    .cfi_def_cfa_offset 64
+; CHECK-NEXT:  .Ltmp4:
+; CHECK-NEXT:    movq %rax, %rbx
+; CHECK-NEXT:    movl {{[-0-9]+}}(%r{{[sb]}}p), %edi # 4-byte Reload
+; CHECK-NEXT:    addl (%rsp), %edi # 4-byte Folded Reload
+; CHECK-NEXT:    callq cleanup@PLT
+; CHECK-NEXT:    movq %rbx, %rdi
+; CHECK-NEXT:    callq _Unwind_Resume@PLT
+  %1 = load i1, ptr @external_bool
+  br i1 %1, label %branchA, label %branchB
+branchA:
+  %valueA = load i32, ptr @externalA
+  %valueC = load i32, ptr @externalC
+  call void asm sideeffect "", "~{rbp},~{rsi},~{rdi},~{rcx},~{rbx},~{r12},~{r13},~{r14},~{r15},~{flags}"()
+  invoke void @maythrow() to label %end unwind label %lpad
+branchB:
+  %valueB = load i32, ptr @externalB
+  %valueD = load i32, ptr @externalD
+  call void asm sideeffect "", "~{rbp},~{rsi},~{rdi},~{rcx},~{rbx},~{r12},~{r13},~{r14},~{r15},~{flags}"()
+  invoke void @maythrow() to label %end unwind label %lpad
+lpad:
+  %phiValue = phi i32 [%valueA, %branchA], [%valueB, %branchB]
+  %phiValue2 = phi i32 [%valueC, %branchA], [%valueD, %branchB]
+  %lp = landingpad { ptr, i32 }
+          cleanup
+  %3 = add i32 %phiValue2, %phiValue
+  call void @cleanup(i32 %3)
+  resume { ptr, i32 } %lp
+end:
+  ret void
+}