[CodeGen] Use first EHLabel as a stop gate for live range shrinking (#114195)

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

@@ -124,15 +124,24 @@ bool LiveRangeShrink::runOnMachineFunction(MachineFunction &MF) {
   for (MachineBasicBlock &MBB : MF) {
     if (MBB.empty())
       continue;
-    bool SawStore = false;
-    BuildInstOrderMap(MBB.begin(), IOM);
+
+    MachineBasicBlock::iterator Next = MBB.begin();
+    if (MBB.isEHPad()) {
+      // Do not track PHIs in IOM when handling EHPads.
+      // Otherwise their uses may be hoisted outside a landingpad range.
+      Next = MBB.SkipPHIsLabelsAndDebug(Next);
+      if (Next == MBB.end())
+        continue;
+    }
+
+    BuildInstOrderMap(Next, IOM);
+    Next = MBB.SkipPHIsLabelsAndDebug(Next);
     UseMap.clear();
+    bool SawStore = false;
 
-    for (MachineBasicBlock::iterator Next = MBB.begin(); Next != MBB.end();) {
+    while (Next != MBB.end()) {
       MachineInstr &MI = *Next;
-      ++Next;
-      if (MI.isPHI() || MI.isDebugOrPseudoInstr())
-        continue;
+      Next = MBB.SkipPHIsLabelsAndDebug(++Next);
       if (MI.mayStore())
         SawStore = true;
 

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
+}