[DebugInfo] Adjust debug info offset for stack arguments in big-endian targets

[yuten]

Summary

Say the function has a 16-bit parameter that is passed via the stack as a 32-bit value.

In big-endian targets, without the adjustment, the offset will be +0 instead of +2, which is incorrect.

[yuten]

Ping

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

if (Reg) {
       Op = MachineOperand::CreateReg(Reg, false);
       IsIndirect = IsDbgDeclare;
     }
   }
 
   if (!Op && N.getNode()) {
     // Check if frame index is available.
     SDValue LCandidate = peekThroughBitcasts(N);
-    if (LoadSDNode *LNode = dyn_cast<LoadSDNode>(LCandidate.getNode()))
+    if (LoadSDNode *LNode = dyn_cast<LoadSDNode>(LCandidate.getNode())) {
       if (FrameIndexSDNode *FINode =
-          dyn_cast<FrameIndexSDNode>(LNode->getBasePtr().getNode()))
+              dyn_cast<FrameIndexSDNode>(LNode->getBasePtr().getNode())) {
         Op = MachineOperand::CreateFI(FINode->getIndex());
+
+        // Adjust offset for big endian architectures
+        if (!MF.getDataLayout().isLittleEndian()) {
+          auto DlBits = Variable->getSizeInBits();
+          auto FIBits = FINode->getValueSizeInBits(0);
+          if (DlBits.hasValue() && !FIBits.isScalable() &&
+              DlBits.getValue() < FIBits.getFixedSize())
+            Expr = DIExpression::prepend(
+                Expr, DIExpression::ApplyOffset,
+                (FIBits.getFixedSize() - DlBits.getValue()) / 8);
+        }
+      }
+    }
   }
 
   if (!Op) {
     // Create a DBG_VALUE for each decomposed value in ArgRegs to cover Reg
     auto splitMultiRegDbgValue = [&](ArrayRef<std::pair<unsigned, TypeSize>>
                                          SplitRegs) {
       unsigned Offset = 0;
       for (auto RegAndSize : SplitRegs) {

llvm/test/DebugInfo/ARM/big-endian-args.ll

+; RUN: llc -mtriple=armebv4t-unknown-unknown -start-after=codegenprepare -o - %s | FileCheck %s
+
+; Verify that the DBG_VALUE p4 and p5 points to an adjusted offset from the frame index due to being big-endian.
+;
+; Generated from the following C code
+;
+;   void foo(int p0, int p1, int p2, int p3, short p4, char p5) {
+;   }
+;
+; compile with -mbig-endian -g -O2 -S -emit-llvm.
+
+; CHECK: @DEBUG_VALUE: foo:p4 <- [DW_OP_plus_uconst 2] [$sp+0]
+; CHECK: @DEBUG_VALUE: foo:p5 <- [DW_OP_plus_uconst 4, DW_OP_plus_uconst 3] [$sp+0]
+
+target datalayout = "E-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armebv4t-unknown-unknown"
+
+; Function Attrs: nofree norecurse nosync nounwind readnone willreturn mustprogress
+define dso_local arm_aapcscc void @foo(i32 %p0, i32 %p1, i32 %p2, i32 %p3, i16 signext %p4, i8 zeroext %p5) local_unnamed_addr #0 !dbg !9 {
+entry:
+  call void @llvm.dbg.value(metadata i32 %p0, metadata !17, metadata !DIExpression()), !dbg !23
+  call void @llvm.dbg.value(metadata i32 %p1, metadata !18, metadata !DIExpression()), !dbg !23
+  call void @llvm.dbg.value(metadata i32 %p2, metadata !19, metadata !DIExpression()), !dbg !23
+  call void @llvm.dbg.value(metadata i32 %p3, metadata !20, metadata !DIExpression()), !dbg !23
+  call void @llvm.dbg.value(metadata i16 %p4, metadata !21, metadata !DIExpression()), !dbg !23
+  call void @llvm.dbg.value(metadata i8 %p5, metadata !22, metadata !DIExpression()), !dbg !23
+  ret void, !dbg !24
+}
+
+; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { nofree norecurse nosync nounwind readnone willreturn mustprogress "frame-pointer"="all" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="arm7tdmi" "target-features"="+armv4t,+soft-float,+strict-align,-aes,-bf16,-crypto,-d32,-dotprod,-fp-armv8,-fp-armv8d16,-fp-armv8d16sp,-fp-armv8sp,-fp16,-fp16fml,-fp64,-fpregs,-fullfp16,-mve,-mve.fp,-neon,-sha2,-thumb-mode,-vfp2,-vfp2sp,-vfp3,-vfp3d16,-vfp3d16sp,-vfp3sp,-vfp4,-vfp4d16,-vfp4d16sp,-vfp4sp" "use-soft-float"="true" }
+attributes #1 = { nofree nosync nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6, !7}
+!llvm.ident = !{!8}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 13.0.0 (https://github.com/llvm/llvm-project 0c330afdfa42370fb50979efd1ee6bcbe9642b6d)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "big-endian-args.c", directory: "/")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{i32 1, !"min_enum_size", i32 4}
+!7 = !{i32 7, !"frame-pointer", i32 2}
+!8 = !{!"clang version 13.0.0 (https://github.com/llvm/llvm-project 0c330afdfa42370fb50979efd1ee6bcbe9642b6d)"}
+!9 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 1, type: !11, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !16)
+!11 = !DISubroutineType(types: !12)
+!12 = !{null, !13, !13, !13, !13, !14, !15}
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !DIBasicType(name: "short", size: 16, encoding: DW_ATE_signed)
+!15 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_unsigned_char)
+!16 = !{!17, !18, !19, !20, !21, !22}
+!17 = !DILocalVariable(name: "p0", arg: 1, scope: !9, file: !1, line: 1, type: !13)
+!18 = !DILocalVariable(name: "p1", arg: 2, scope: !9, file: !1, line: 1, type: !13)
+!19 = !DILocalVariable(name: "p2", arg: 3, scope: !9, file: !1, line: 1, type: !13)
+!20 = !DILocalVariable(name: "p3", arg: 4, scope: !9, file: !1, line: 1, type: !13)
+!21 = !DILocalVariable(name: "p4", arg: 5, scope: !9, file: !1, line: 1, type: !14)
+!22 = !DILocalVariable(name: "p5", arg: 6, scope: !9, file: !1, line: 1, type: !15)
+!23 = !DILocation(line: 0, scope: !9)
+!24 = !DILocation(line: 2, column: 1, scope: !9)