[DebugInfo] Allow spill slots in call site parameter descriptions

[vsk]

Summary

Allow call site paramter descriptions to reference spill slots. Spill
slots are not visible to high-level LLVM IR, so they can safely be
referenced during entry value evaluation (as they cannot be clobbered by
some other function).

This gives a 5% increase in the number of call site parameter DIEs in an
LTO x86_64 build of the xnu kernel.

This reverts commit eb4c98ca3d2590bad9f6542afbf3a7824d2b53fa (
[DebugInfo] Exclude memory location values as parameter entry values),
effectively reintroducing the portion of D60716 which dealt with memory
locations (authored by Djordje, Nikola, Ananth, and Ivan).

This partially addresses llvm.org/PR43343. However, not all memory
operands forwarded to callees live in spill slots. In the xnu build, it
may be possible to use an escape analysis to increase the number of call
site parameter by another 15% (more details in PR43343).

llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp

if (HasComplexExpression && DwarfRegs.size() > 1) {
     LocationKind = Unknown;
     return false;
   }
 
   // Handle simple register locations. If we are supposed to emit
   // a call site parameter expression and if that expression is just a register
   // location, emit it with addBReg and offset 0, because we should emit a DWARF
   // expression representing a value, rather than a location.
-  if (!isMemoryLocation() && !HasComplexExpression &&
-      (!isParameterValue() || isEntryValue())) {
+  if (!isMemoryLocation() && !HasComplexExpression && (!isParameterValue() ||
+                                                       isEntryValue())) {
     for (auto &Reg : DwarfRegs) {
       if (Reg.DwarfRegNo >= 0)
         addReg(Reg.DwarfRegNo, Reg.Comment);
       addOpPiece(Reg.Size);
     }
 
     if (isEntryValue())
       finalizeEntryValue();
while (ExprCursor) {
     case dwarf::DW_OP_shra:
     case dwarf::DW_OP_lit0:
     case dwarf::DW_OP_not:
     case dwarf::DW_OP_dup:
       emitOp(OpNum);
       break;
     case dwarf::DW_OP_deref:
       assert(!isRegisterLocation());
-      // For more detailed explanation see llvm.org/PR43343.
-      assert(!isParameterValue() && "Parameter entry values should not be "
-                                    "dereferenced due to safety reasons.");
       if (!isMemoryLocation() && ::isMemoryLocation(ExprCursor))
         // Turning this into a memory location description makes the deref
         // implicit.
         LocationKind = Memory;
       else
         emitOp(dwarf::DW_OP_deref);
       break;
     case dwarf::DW_OP_constu:

llvm/lib/CodeGen/TargetInstrInfo.cpp

TargetInstrInfo::describeLoadedValue(const MachineInstr &MI) const {
   DIExpression *Expr = DIExpression::get(MF->getFunction().getContext(), {});
   int64_t Offset;
 
   if (auto DestSrc = isCopyInstr(MI)) {
     return ParamLoadedValue(*DestSrc->Source, Expr);
   } else if (auto DestSrc = isAddImmediate(MI, Offset)) {
     Expr = DIExpression::prepend(Expr, DIExpression::ApplyOffset, Offset);
     return ParamLoadedValue(*DestSrc->Source, Expr);
+  } else if (MI.hasOneMemOperand()) {
+    // Only describe memory which provably does not escape the function. As
+    // described in llvm.org/PR43343, escaped memory may be clobbered by the
+    // callee (or by another thread).
+    const auto &TII = MF->getSubtarget().getInstrInfo();
+    const MachineFrameInfo &MFI = MF->getFrameInfo();
+    const MachineMemOperand *MMO = MI.memoperands()[0];
+    const PseudoSourceValue *PSV = MMO->getPseudoValue();
+
+    // If the address points to "special" memory (e.g. a spill slot), it's
+    // sufficient to check that it isn't aliased by any high-level IR value.
+    if (!PSV || PSV->mayAlias(&MFI))
+      return None;
+
+    const auto &TRI = MF->getSubtarget().getRegisterInfo();
+    const MachineOperand *BaseOp;
+    if (!TII->getMemOperandWithOffset(MI, BaseOp, Offset, TRI))
+      return None;
+
+    Expr = DIExpression::prepend(Expr, DIExpression::DerefAfter, Offset);
+    return ParamLoadedValue(*BaseOp, Expr);
   }
 
   return None;
 }
 
 /// Both DefMI and UseMI must be valid.  By default, call directly to the
 /// itinerary. This may be overriden by the target.
 int TargetInstrInfo::getOperandLatency(const InstrItineraryData *ItinData,

llvm/test/DebugInfo/MIR/X86/dbg-call-site-spilled-arg.mir

+# Check that llvm can describe a call site parameter which resides in a spill slot.
+#
+# RUN: llc -debug-entry-values -start-after=machineverifier -filetype=obj %s -o - | llvm-dwarfdump - | FileCheck %s
+# 
+# Command:
+# $ ~/src/builds/llvm-project-master-RA/bin/clang -g -Xclang -femit-debug-entry-values -O2 -c -o spill.o spill.cc -mllvm -stop-before=machineverifier -o spill.mir
+#
+# Source:
+## extern void callee(int);
+## 
+## #define FORCE_SPILL()                                                          \
+##   asm volatile(""                                                              \
+##                :                                                               \
+##                :                                                               \
+##                : "rax", "rbx", "rcx", "rdx", "rsi", "rdi", "rbp", "r8", "r9",  \
+##                  "r10", "r11", "r12", "r13", "r14", "r15")
+## 
+## __attribute__((disable_tail_calls)) void caller(int x) {
+##   FORCE_SPILL();
+##   callee(x);
+## }
+
+# CHECK-LABEL: DW_TAG_call_site_parameter
+# CHECK-NEXT:    DW_AT_location (DW_OP_reg5 RDI)
+# CHECK-NEXT:    DW_AT_call_value (DW_OP_fbreg -44, DW_OP_deref)
+
+--- |
+  ; ModuleID = 'spill.cc'
+  source_filename = "spill.cc"
+  target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+  target triple = "x86_64-apple-macosx10.14.0"
+  
+  ; Function Attrs: ssp uwtable
+  define void @_Z6calleri(i32 %x) local_unnamed_addr #0 !dbg !13 {
+  entry:
+    call void @llvm.dbg.value(metadata i32 %x, metadata !15, metadata !DIExpression()), !dbg !16
+    call void asm sideeffect "", "~{rax},~{rbx},~{rcx},~{rdx},~{rsi},~{rdi},~{rbp},~{r8},~{r9},~{r10},~{r11},~{r12},~{r13},~{r14},~{r15},~{dirflag},~{fpsr},~{flags}"(), !dbg !17, !srcloc !18
+    call void @_Z6calleei(i32 %x), !dbg !19
+    ret void, !dbg !20
+  }
+  
+  declare !dbg !4 void @_Z6calleei(i32) local_unnamed_addr
+  
+  ; Function Attrs: nounwind readnone speculatable willreturn
+  declare void @llvm.dbg.value(metadata, metadata, metadata)
+  
+  ; Function Attrs: nounwind
+  declare void @llvm.stackprotector(i8*, i8**)
+  
+  attributes #0 = { "disable-tail-calls"="true" "frame-pointer"="all" }
+  
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!8, !9, !10, !11}
+  !llvm.ident = !{!12}
+  
+  !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 10.0.0 ([e-mail]:llvm/llvm-project.git 132f768649d8f21d577ee220e5e084904874cb3d)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
+  !1 = !DIFile(filename: "spill.cc", directory: "/Users/vsk/tmp/param-analysis")
+  !2 = !{}
+  !3 = !{!4}
+  !4 = !DISubprogram(name: "callee", linkageName: "_Z6calleei", scope: !1, file: !1, line: 1, type: !5, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+  !5 = !DISubroutineType(types: !6)
+  !6 = !{null, !7}
+  !7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !8 = !{i32 2, !"Dwarf Version", i32 4}
+  !9 = !{i32 2, !"Debug Info Version", i32 3}
+  !10 = !{i32 1, !"wchar_size", i32 4}
+  !11 = !{i32 7, !"PIC Level", i32 2}
+  !12 = !{!"clang version 10.0.0 ([e-mail]:llvm/llvm-project.git 132f768649d8f21d577ee220e5e084904874cb3d)"}
+  !13 = distinct !DISubprogram(name: "caller", linkageName: "_Z6calleri", scope: !1, file: !1, line: 10, type: !5, scopeLine: 10, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !14)
+  !14 = !{!15}
+  !15 = !DILocalVariable(name: "x", arg: 1, scope: !13, file: !1, line: 10, type: !7, flags: DIFlagArgumentNotModified)
+  !16 = !DILocation(line: 0, scope: !13)
+  !17 = !DILocation(line: 11, column: 3, scope: !13)
+  !18 = !{i32 -2147469811}
+  !19 = !DILocation(line: 12, column: 3, scope: !13)
+  !20 = !DILocation(line: 13, column: 1, scope: !13)
+
+...
+---
+name:            _Z6calleri
+alignment:       16
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+hasWinCFI:       false
+registers:       []
+liveins:
+  - { reg: '$edi', virtual-reg: '' }
+frameInfo:
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       56
+  offsetAdjustment: -56
+  maxAlignment:    4
+  adjustsStack:    true
+  hasCalls:        true
+  stackProtector:  ''
+  maxCallFrameSize: 0
+  cvBytesOfCalleeSavedRegisters: 40
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+  localFrameSize:  0
+  savePoint:       ''
+  restorePoint:    ''
+fixedStack:
+  - { id: 0, type: spill-slot, offset: -56, size: 8, alignment: 8, stack-id: default, 
+      callee-saved-register: '$rbx', callee-saved-restored: true, debug-info-variable: '', 
+      debug-info-expression: '', debug-info-location: '' }
+  - { id: 1, type: spill-slot, offset: -48, size: 8, alignment: 16, stack-id: default, 
+      callee-saved-register: '$r12', callee-saved-restored: true, debug-info-variable: '', 
+      debug-info-expression: '', debug-info-location: '' }
+  - { id: 2, type: spill-slot, offset: -40, size: 8, alignment: 8, stack-id: default, 
+      callee-saved-register: '$r13', callee-saved-restored: true, debug-info-variable: '', 
+      debug-info-expression: '', debug-info-location: '' }
+  - { id: 3, type: spill-slot, offset: -32, size: 8, alignment: 16, stack-id: default, 
+      callee-saved-register: '$r14', callee-saved-restored: true, debug-info-variable: '', 
+      debug-info-expression: '', debug-info-location: '' }
+  - { id: 4, type: spill-slot, offset: -24, size: 8, alignment: 8, stack-id: default, 
+      callee-saved-register: '$r15', callee-saved-restored: true, debug-info-variable: '', 
+      debug-info-expression: '', debug-info-location: '' }
+  - { id: 5, type: spill-slot, offset: -16, size: 8, alignment: 16, stack-id: default, 
+      callee-saved-register: '', callee-saved-restored: true, debug-info-variable: '', 
+      debug-info-expression: '', debug-info-location: '' }
+stack:
+  - { id: 0, name: '', type: spill-slot, offset: -60, size: 4, alignment: 4, 
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+callSites:
+  - { bb: 0, offset: 23, fwdArgRegs: 
+      - { arg: 0, reg: '$edi' } }
+constants:       []
+machineFunctionInfo: {}
+body:             |
+  bb.0.entry:
+    liveins: $edi, $r15, $r14, $r13, $r12, $rbx
+  
+    DBG_VALUE $edi, $noreg, !15, !DIExpression(), debug-location !16
+    frame-setup PUSH64r killed $rbp, implicit-def $rsp, implicit $rsp
+    CFI_INSTRUCTION def_cfa_offset 16
+    CFI_INSTRUCTION offset $rbp, -16
+    $rbp = frame-setup MOV64rr $rsp
+    CFI_INSTRUCTION def_cfa_register $rbp
+    frame-setup PUSH64r killed $r15, implicit-def $rsp, implicit $rsp
+    frame-setup PUSH64r killed $r14, implicit-def $rsp, implicit $rsp
+    frame-setup PUSH64r killed $r13, implicit-def $rsp, implicit $rsp
+    frame-setup PUSH64r killed $r12, implicit-def $rsp, implicit $rsp
+    frame-setup PUSH64r killed $rbx, implicit-def $rsp, implicit $rsp
+    frame-setup PUSH64r undef $rax, implicit-def $rsp, implicit $rsp
+    CFI_INSTRUCTION offset $rbx, -56
+    CFI_INSTRUCTION offset $r12, -48
+    CFI_INSTRUCTION offset $r13, -40
+    CFI_INSTRUCTION offset $r14, -32
+    CFI_INSTRUCTION offset $r15, -24
+    MOV32mr $rbp, 1, $noreg, -44, $noreg, $edi :: (store 4 into %stack.0)
+    DBG_VALUE $rbp, 0, !15, !DIExpression(DW_OP_constu, 44, DW_OP_minus), debug-location !16
+    INLINEASM &"", 1, 12, implicit-def dead early-clobber $rax, 12, implicit-def dead early-clobber $rbx, 12, implicit-def dead early-clobber $rcx, 12, implicit-def dead early-clobber $rdx, 12, implicit-def dead early-clobber $rsi, 12, implicit-def dead early-clobber $rdi, 12, implicit-def early-clobber $rbp, 12, implicit-def dead early-clobber $r8, 12, implicit-def dead early-clobber $r9, 12, implicit-def dead early-clobber $r10, 12, implicit-def dead early-clobber $r11, 12, implicit-def dead early-clobber $r12, 12, implicit-def dead early-clobber $r13, 12, implicit-def dead early-clobber $r14, 12, implicit-def dead early-clobber $r15, 12, implicit-def dead early-clobber $df, 12, implicit-def early-clobber $fpsw, 12, implicit-def dead early-clobber $eflags, !18, debug-location !17
+    DBG_VALUE $edi, $noreg, !15, !DIExpression(DW_OP_LLVM_entry_value, 1), debug-location !16
+    $edi = MOV32rm $rbp, 1, $noreg, -44, $noreg :: (load 4 from %stack.0)
+    DBG_VALUE $edi, $noreg, !15, !DIExpression(), debug-location !16
+    CALL64pcrel32 @_Z6calleei, csr_64, implicit $rsp, implicit $ssp, implicit $edi, implicit-def $rsp, implicit-def $ssp, debug-location !19
+    DBG_VALUE $edi, $noreg, !15, !DIExpression(DW_OP_LLVM_entry_value, 1), debug-location !16
+    $rsp = frame-destroy ADD64ri8 $rsp, 8, implicit-def dead $eflags, debug-location !20
+    $rbx = frame-destroy POP64r implicit-def $rsp, implicit $rsp, debug-location !20
+    $r12 = frame-destroy POP64r implicit-def $rsp, implicit $rsp, debug-location !20
+    $r13 = frame-destroy POP64r implicit-def $rsp, implicit $rsp, debug-location !20
+    $r14 = frame-destroy POP64r implicit-def $rsp, implicit $rsp, debug-location !20
+    $r15 = frame-destroy POP64r implicit-def $rsp, implicit $rsp, debug-location !20
+    $rbp = frame-destroy POP64r implicit-def $rsp, implicit $rsp, debug-location !20
+    RETQ debug-location !20
+
+...