[Statepoint] Handle `undef` operands in statepoint.

[dantrushin]

Summary

Currently when spilling statepoint register operands in FixupStatepoints
we do not pay attention that it might be undef. We just generate a
spill, which may lead to verifier error because we have use without a def.

To handle it, let FixupStateponts ignore undef register operands
completely and change them to some constant value when generating
stack map. Use same value as used by ISel for this purpose (0xFEFEFEFE).

[reames]

LGTM w/an MIR test case added before submission.

[dantrushin]

Add test case;

[arsenm]

llvm/lib/CodeGen/StackMaps.cpp

239

What is the intended representation of undef here? This will be replaced later (down at line 485) with ConstantIndex. Why can't this stay as Register?

llvm/lib/CodeGen/FixupStatepointCallerSaved.cpp

bool findRegistersToSpill() {
     for (const auto &Def : MI.defs())
       GCRegs.insert(Def.getReg());
 
     SmallSet<Register, 8> VisitedRegs;
     for (unsigned Idx = StatepointOpers(&MI).getVarIdx(),
                   EndIdx = MI.getNumOperands();
          Idx < EndIdx; ++Idx) {
       MachineOperand &MO = MI.getOperand(Idx);
-      if (!MO.isReg() || MO.isImplicit())
+      // Leave `undef` operands as is, StackMaps will rewrite them
+      // into a constant.
+      if (!MO.isReg() || MO.isImplicit() || MO.isUndef())
         continue;
       Register Reg = MO.getReg();
       assert(Reg.isPhysical() && "Only physical regs are expected");
 
       if (isCalleeSaved(Reg) && (AllowGCPtrInCSR || !is_contained(GCRegs, Reg)))
         continue;
 
       LLVM_DEBUG(dbgs() << "Will spill " << printReg(Reg, &TRI) << " at index "

llvm/lib/CodeGen/StackMaps.cpp

StackMaps::parseOperand(MachineInstr::const_mop_iterator MOI,
   // The stack map also records the size of a spill slot that can hold the
   // register content. (The runtime can track the actual size of the data type
   // if it needs to.)
   if (MOI->isReg()) {
     // Skip implicit registers (this includes our scratch registers)
     if (MOI->isImplicit())
       return ++MOI;
 
+    if (MOI->isUndef()) {
+      // Record `undef` register as constant. Use same value as ISel uses.
+      Locs.emplace_back(Location::Constant, sizeof(int64_t), 0, 0xFEFEFEFE);
+      return ++MOI;
+    }
+
     assert(Register::isPhysicalRegister(MOI->getReg()) &&
            "Virtreg operands should have been rewritten before now.");
     const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(MOI->getReg());
     assert(!MOI->getSubReg() && "Physical subreg still around.");
 
     unsigned Offset = 0;
     unsigned DwarfRegNum = getDwarfRegNum(MOI->getReg(), TRI);
     unsigned LLVMRegNum = *TRI->getLLVMRegNum(DwarfRegNum, false);

llvm/test/CodeGen/X86/statepoint-fixup-undef.mir

+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -x mir -run-pass fixup-statepoint-caller-saved -verify-machineinstrs < %s | FileCheck %s
+# RUN: llc -x mir -start-before fixup-statepoint-caller-saved -verify-machineinstrs < %s | FileCheck %s -check-prefix=STACKMAP
+
+--- |
+  ; ModuleID = 'undef.ll'
+  source_filename = "test_undef.ll"
+  target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+  target triple = "x86_64-unknown-linux-gnu"
+
+  define void @test_undef(i8 addrspace(1)* %arg1, i8 addrspace(1)* %arg2, i8 addrspace(1)* %arg3, i8 addrspace(1)* %arg4) #0 gc "statepoint-example" {
+  bb:
+    %tmp1 = lshr i32 0, undef
+    %tmp2 = load atomic i32, i32 addrspace(1)* undef unordered, align 8
+    %tmp3 = load atomic i32, i32 addrspace(1)* undef unordered, align 8
+    br label %bb7
+
+  bb7:                                              ; preds = %bb
+    %tmp4 = icmp slt i32 %tmp3, undef
+    %tmp5 = select i1 %tmp4, i32 6, i32 undef
+    %tmp6 = add i32 %tmp5, %tmp2
+    %tmp7 = call i8 addrspace(1)* @wombat()
+    %tmp20 = call token (i64, i32, void (i8 addrspace(1)*, i32, i32, i8 addrspace(1)*, i32)*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidp1i8i32i32p1i8i32f(i64 2, i32 5, void (i8 addrspace(1)*, i32, i32, i8 addrspace(1)*, i32)* nonnull @hoge, i32 5, i32 0, i8 addrspace(1)* %arg3, i32 %tmp2, i32 %tmp6, i8 addrspace(1)* %tmp7, i32 0, i32 0, i32 0) [ "deopt"(i8 addrspace(1)* %arg2, i8 addrspace(1)* %arg1, i8 addrspace(1)* %arg3, i8 addrspace(1)* %arg4, i32 %tmp2, i32 %tmp1, i32 %tmp5), "gc-live"() ]
+    ret void
+  }
+
+  declare void @hoge(i8 addrspace(1)*, i32, i32, i8 addrspace(1)*, i32) #0
+
+  declare i8 addrspace(1)* @wombat() #0
+
+  ; Function Attrs: nounwind readonly
+  declare i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token, i32 immarg, i32 immarg) #1
+
+  declare token @llvm.experimental.gc.statepoint.p0f_isVoidp1i8i32i32p1i8i32f(i64 immarg, i32 immarg, void (i8 addrspace(1)*, i32, i32, i8 addrspace(1)*, i32)*, i32 immarg, i32 immarg, ...) #0
+
+  attributes #0 = { "target-cpu"="broadwell" }
+  attributes #1 = { nounwind readonly "target-cpu"="broadwell" }
+
+...
+---
+name:            test_undef
+alignment:       16
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+hasWinCFI:       false
+registers:       []
+liveins:
+  - { reg: '$rdi', virtual-reg: '' }
+  - { reg: '$rsi', virtual-reg: '' }
+  - { reg: '$rdx', virtual-reg: '' }
+  - { reg: '$rcx', virtual-reg: '' }
+frameInfo:
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       0
+  offsetAdjustment: 0
+  maxAlignment:    8
+  adjustsStack:    false
+  hasCalls:        true
+  stackProtector:  ''
+  maxCallFrameSize: 4294967295
+  cvBytesOfCalleeSavedRegisters: 0
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+  localFrameSize:  0
+  savePoint:       ''
+  restorePoint:    ''
+fixedStack:      []
+stack:
+  - { id: 0, name: '', type: default, offset: 0, size: 8, alignment: 8,
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 1, name: '', type: default, offset: 0, size: 8, alignment: 8,
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 2, name: '', type: default, offset: 0, size: 8, alignment: 8,
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 3, name: '', type: default, offset: 0, size: 8, alignment: 8,
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+callSites:       []
+debugValueSubstitutions: []
+constants:       []
+machineFunctionInfo: {}
+body:             |
+  ; CHECK-LABEL: name: test_undef
+  ; CHECK: bb.0.bb:
+  ; CHECK:   successors: %bb.1(0x80000000)
+  ; CHECK:   liveins: $rcx, $rdi, $rdx, $rsi
+  ; CHECK:   renamable $r15 = COPY $rcx
+  ; CHECK:   renamable $r14 = COPY $rdx
+  ; CHECK:   renamable $r13 = COPY $rsi
+  ; CHECK:   renamable $r12 = COPY $rdi
+  ; CHECK:   renamable $ebx = MOV32rm undef renamable $rax, 1, $noreg, 0, $noreg, implicit-def $rbx :: (load unordered 4 from `i32 addrspace(1)* undef`, align 8, addrspace 1)
+  ; CHECK: bb.1.bb7:
+  ; CHECK:   liveins: $rbx, $r12, $r13, $r14, $r15
+  ; CHECK:   renamable $ebp = LEA64_32r renamable $rbx, 1, $noreg, 6, $noreg
+  ; CHECK:   ADJCALLSTACKDOWN64 0, 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp
+  ; CHECK:   CALL64pcrel32 target-flags(x86-plt) @wombat, csr_64, implicit $rsp, implicit $ssp, implicit-def $rsp, implicit-def $ssp, implicit-def $rax
+  ; CHECK:   ADJCALLSTACKUP64 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp
+  ; CHECK:   MOV64mr %stack.0, 1, $noreg, 0, $noreg, killed renamable $r13 :: (store 8 into %stack.0)
+  ; CHECK:   MOV64mr %stack.1, 1, $noreg, 0, $noreg, killed renamable $r12 :: (store 8 into %stack.1)
+  ; CHECK:   MOV64mr %stack.2, 1, $noreg, 0, $noreg, renamable $r14 :: (store 8 into %stack.2)
+  ; CHECK:   MOV64mr %stack.3, 1, $noreg, 0, $noreg, killed renamable $r15 :: (store 8 into %stack.3)
+  ; CHECK:   ADJCALLSTACKDOWN64 0, 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp
+  ; CHECK:   $rdi = COPY killed renamable $r14
+  ; CHECK:   $esi = COPY renamable $ebx
+  ; CHECK:   $edx = COPY killed renamable $ebp
+  ; CHECK:   $rcx = COPY killed renamable $rax
+  ; CHECK:   $r8d = MOV32r0 implicit-def dead $eflags
+  ; CHECK:   STATEPOINT 2, 5, 5, undef renamable $rax, $rdi, $esi, $edx, $rcx, killed $r8d, 2, 0, 2, 0, 2, 7, 1, 8, %stack.0, 0, 1, 8, %stack.1, 0, 1, 8, %stack.2, 0, 1, 8, %stack.3, 0, renamable $ebx, undef renamable $eax, 2, 6, 2, 0, 2, 0, 2, 0, csr_64, implicit-def $rsp, implicit-def $ssp, implicit killed $rbx :: (volatile load store 8 on %stack.0), (volatile load store 8 on %stack.1), (volatile load store 8 on %stack.2), (volatile load store 8 on %stack.3)
+  ; CHECK:   ADJCALLSTACKUP64 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp
+  ; CHECK:   RET 0
+  ; STACKMAP-LABEL: __LLVM_StackMaps:
+  ; STACKMAP: .byte 3
+  ; STACKMAP: .byte 0
+  ; STACKMAP: .short  0
+  ; STACKMAP: .long 1
+  ; STACKMAP: .long 1
+  ; STACKMAP: .long 1
+  ; STACKMAP: .quad test_undef
+  ; STACKMAP: .quad 88
+  ; STACKMAP: .quad 1
+  ; STACKMAP: .quad 4278124286
+  ; STACKMAP: .quad 2
+  ; STACKMAP: .long .Ltmp0-test_undef
+  ; STACKMAP: .short  0
+  ; STACKMAP: .short  10
+  ; STACKMAP: .byte 4
+  ; STACKMAP: .byte 0
+  ; STACKMAP: .short  8
+  ; STACKMAP: .short  0
+  ; STACKMAP: .short  0
+  ; STACKMAP: .long 0
+  ; STACKMAP: .byte 4
+  ; STACKMAP: .byte 0
+  ; STACKMAP: .short  8
+  ; STACKMAP: .short  0
+  ; STACKMAP: .short  0
+  ; STACKMAP: .long 0
+  ; STACKMAP: .byte 4
+  ; STACKMAP: .byte 0
+  ; STACKMAP: .short  8
+  ; STACKMAP: .short  0
+  ; STACKMAP: .short  0
+  ; STACKMAP: .long 7
+  ; STACKMAP: .byte 3
+  ; STACKMAP: .byte 0
+  ; STACKMAP: .short  8
+  ; STACKMAP: .short  7
+  ; STACKMAP: .short  0
+  ; STACKMAP: .long 32
+  ; STACKMAP: .byte 3
+  ; STACKMAP: .byte 0
+  ; STACKMAP: .short  8
+  ; STACKMAP: .short  7
+  ; STACKMAP: .short  0
+  ; STACKMAP: .long 24
+  ; STACKMAP: .byte 3
+  ; STACKMAP: .byte 0
+  ; STACKMAP: .short  8
+  ; STACKMAP: .short  7
+  ; STACKMAP: .short  0
+  ; STACKMAP: .long 16
+  ; STACKMAP: .byte 3
+  ; STACKMAP: .byte 0
+  ; STACKMAP: .short  8
+  ; STACKMAP: .short  7
+  ; STACKMAP: .short  0
+  ; STACKMAP: .long 8
+  ; STACKMAP: .byte 1
+  ; STACKMAP: .byte 0
+  ; STACKMAP: .short  4
+  ; STACKMAP: .short  3
+  ; STACKMAP: .short  0
+  ; STACKMAP: .long 0
+  ;      This is entry we're looking for, reference to constant pool entry 0xFEFEFEFE
+  ; STACKMAP: .byte 5
+  ; STACKMAP: .byte 0
+  ; STACKMAP: .short  8
+  ; STACKMAP: .short  0
+  ; STACKMAP: .short  0
+  ; STACKMAP: .long 0
+  ; STACKMAP: .byte 4
+  ; STACKMAP: .byte 0
+  ; STACKMAP: .short  8
+  ; STACKMAP: .short  0
+  ; STACKMAP: .short  0
+  ; STACKMAP: .long 6
+  ; STACKMAP: .p2align  3
+  ; STACKMAP: .short  0
+  ; STACKMAP: .short  0
+  ; STACKMAP: .p2align  3
+  bb.0.bb:
+    successors: %bb.1(0x80000000)
+    liveins: $rcx, $rdi, $rdx, $rsi
+
+    renamable $r15 = COPY $rcx
+    renamable $r14 = COPY $rdx
+    renamable $r13 = COPY $rsi
+    renamable $r12 = COPY $rdi
+    renamable $ebx = MOV32rm undef renamable $rax, 1, $noreg, 0, $noreg, implicit-def $rbx :: (load unordered 4 from `i32 addrspace(1)* undef`, align 8, addrspace 1)
+
+  bb.1.bb7:
+    liveins: $rbx, $r12, $r13, $r14, $r15
+
+    renamable $ebp = LEA64_32r renamable $rbx, 1, $noreg, 6, $noreg
+    ADJCALLSTACKDOWN64 0, 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp
+    CALL64pcrel32 target-flags(x86-plt) @wombat, csr_64, implicit $rsp, implicit $ssp, implicit-def $rsp, implicit-def $ssp, implicit-def $rax
+    ADJCALLSTACKUP64 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp
+    MOV64mr %stack.0, 1, $noreg, 0, $noreg, killed renamable $r13 :: (store 8 into %stack.0)
+    MOV64mr %stack.1, 1, $noreg, 0, $noreg, killed renamable $r12 :: (store 8 into %stack.1)
+    MOV64mr %stack.2, 1, $noreg, 0, $noreg, renamable $r14 :: (store 8 into %stack.2)
+    MOV64mr %stack.3, 1, $noreg, 0, $noreg, killed renamable $r15 :: (store 8 into %stack.3)
+    ADJCALLSTACKDOWN64 0, 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp
+    $rdi = COPY killed renamable $r14
+    $esi = COPY renamable $ebx
+    $edx = COPY killed renamable $ebp
+    $rcx = COPY killed renamable $rax
+    $r8d = MOV32r0 implicit-def dead $eflags
+    STATEPOINT 2, 5, 5, undef renamable $rax, $rdi, $esi, $edx, $rcx, killed $r8d, 2, 0, 2, 0, 2, 7, 1, 8, %stack.0, 0, 1, 8, %stack.1, 0, 1, 8, %stack.2, 0, 1, 8, %stack.3, 0, renamable $ebx, undef renamable $eax, 2, 6, 2, 0, 2, 0, 2, 0, csr_64, implicit-def $rsp, implicit-def $ssp, implicit killed $rbx :: (volatile load store 8 on %stack.0), (volatile load store 8 on %stack.1), (volatile load store 8 on %stack.2), (volatile load store 8 on %stack.3)
+    ADJCALLSTACKUP64 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp
+    RET 0
+
+...
+