[Debug] Look through bitcasts to find argument registers

[olista01]

Summary

On targets where f32 is not legal, we have to look through a BITCAST SDNode to find the register that an argument is stored in when emitting debug info, or we will not be able to emit a DW_AT_location for it.

[olista01]

+Eric

Ping?

[dblaikie]

Looks plausible, but I haven't done much with the debug info location side of things - wouldn't mind a second opinion.

test/DebugInfo/ARM/float-args.ll

3 ↗

(On Diff #35215)

Usually I run the llc and dwarfdump commands together, rather than using a temp file:

llc -o - | llvm-dwarfdump - | FileCheck

(plus all the other usual args)

9 ↗

(On Diff #35215)

Do you need a use of 'p' for this test case, or just the argument 'p'? (do you need the arithmetic - or can you just "return p" (or sometimes I'll use a stub-function to ensure a use:

void f1(float);
void f2(float p) {
  f1(p);
}

to make it clear that a use is necessary (& the call can't be optimized away) but it doesn't really matter what that use is))

[olista01]

Simplified test

[olista01]

Ping

[olista01]

Ping

[aprantl]

This looks like a strict improvement.

llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

if (!F->optForSize() ||
       return Res;
     }
   }
 
   // Otherwise, expand to a libcall.
   return DAG.getNode(ISD::FPOWI, DL, LHS.getValueType(), LHS, RHS);
 }
 
-// getTruncatedArgReg - Find underlying register used for an truncated
-// argument.
-static unsigned getTruncatedArgReg(const SDValue &N) {
-  if (N.getOpcode() != ISD::TRUNCATE)
+// getUnderlyingArgReg - Find underlying register used for a truncated or
+// bitcasted argument.
+static unsigned getUnderlyingArgReg(const SDValue &N) {
+  switch (N.getOpcode()) {
+  case ISD::CopyFromReg:
+    return cast<RegisterSDNode>(N.getOperand(1))->getReg();
+  case ISD::BITCAST:
+  case ISD::AssertZext:
+  case ISD::AssertSext:
+  case ISD::TRUNCATE:
+    return getUnderlyingArgReg(N.getOperand(0));
+  default:
     return 0;
-
-  const SDValue &Ext = N.getOperand(0);
-  if (Ext.getOpcode() == ISD::AssertZext ||
-      Ext.getOpcode() == ISD::AssertSext) {
-    const SDValue &CFR = Ext.getOperand(0);
-    if (CFR.getOpcode() == ISD::CopyFromReg)
-      return cast<RegisterSDNode>(CFR.getOperand(1))->getReg();
-    if (CFR.getOpcode() == ISD::TRUNCATE)
-      return getTruncatedArgReg(CFR);
   }
-  return 0;
 }
 
 /// EmitFuncArgumentDbgValue - If the DbgValueInst is a dbg_value of a function
 /// argument, create the corresponding DBG_VALUE machine instruction for it now.
 /// At the end of instruction selection, they will be inserted to the entry BB.
 bool SelectionDAGBuilder::EmitFuncArgumentDbgValue(
     const Value *V, DILocalVariable *Variable, DIExpression *Expr,
     DILocation *DL, int64_t Offset, bool IsIndirect, const SDValue &N) {
if (!Variable->getScope()->getSubprogram()->describes(MF.getFunction()))
     return false;
 
   Optional<MachineOperand> Op;
   // Some arguments' frame index is recorded during argument lowering.
   if (int FI = FuncInfo.getArgumentFrameIndex(Arg))
     Op = MachineOperand::CreateFI(FI);
 
   if (!Op && N.getNode()) {
-    unsigned Reg;
-    if (N.getOpcode() == ISD::CopyFromReg)
-      Reg = cast<RegisterSDNode>(N.getOperand(1))->getReg();
-    else
-      Reg = getTruncatedArgReg(N);
+    unsigned Reg = getUnderlyingArgReg(N);
     if (Reg && TargetRegisterInfo::isVirtualRegister(Reg)) {
       MachineRegisterInfo &RegInfo = MF.getRegInfo();
       unsigned PR = RegInfo.getLiveInPhysReg(Reg);
       if (PR)
         Reg = PR;
     }
     if (Reg)
       Op = MachineOperand::CreateReg(Reg, false);

llvm/trunk/test/DebugInfo/ARM/float-args.ll

+; RUN: %llc_dwarf -filetype=obj -mattr=+vfp2 -float-abi=hard < %s | llvm-dwarfdump -debug-dump=info - | FileCheck %s
+; RUN: %llc_dwarf -filetype=obj -mattr=-vfp2 -float-abi=soft < %s | llvm-dwarfdump -debug-dump=info - | FileCheck %s
+; REQUIRES: object-emission
+
+; Generated by clang -O1 -g from the following C source:
+; float foo(float p) {
+;   return p;
+; }
+
+; When using the soft-float calling convention, we have to look through a
+; bitcast to find the register which contains the argument.
+
+; CHECK:     0x{{[0-9a-f]*}}:  DW_TAG_formal_parameter
+; CHECK-NEXT:                      DW_AT_location
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armv7--none-eabi"
+
+define float @foo(float %p) {
+entry:
+  tail call void @llvm.dbg.value(metadata float %p, i64 0, metadata !9, metadata !15), !dbg !16
+  ret float %p, !dbg !18
+}
+
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!10, !11}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.8.0", isOptimized: true, runtimeVersion: 0, emissionKind: 1, enums: !2, subprograms: !3)
+!1 = !DIFile(filename: "test.c", directory: "")
+!2 = !{}
+!3 = !{!4}
+!4 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 1, type: !5, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, function: float (float)* @foo, variables: !8)
+!5 = !DISubroutineType(types: !6)
+!6 = !{!7, !7}
+!7 = !DIBasicType(name: "float", size: 32, align: 32, encoding: DW_ATE_float)
+!8 = !{!9}
+!9 = !DILocalVariable(name: "p", arg: 1, scope: !4, file: !1, line: 1, type: !7)
+!10 = !{i32 2, !"Dwarf Version", i32 4}
+!11 = !{i32 2, !"Debug Info Version", i32 3}
+!15 = !DIExpression()
+!16 = !DILocation(line: 1, column: 17, scope: !4)
+!17 = !DILocation(line: 2, column: 12, scope: !4)
+!18 = !DILocation(line: 2, column: 3, scope: !4)