A fix for PR21176.

DW_OP_const <const> doesn't describe a constant value, but a value at a constant address.
The proper way to describe a constant value is DW_OP_constu <const>, DW_OP_stack_value.
Added DW_OP_stack_value to the stack.

Marked incorrect-variable-debugloc1.ll to xfail for PowerPC64, while the the failure (PR21881)
is being investigated.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224098 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 230ea4651823631335ccda2866af90d9ac41b5e0..b7e9d656e901e96577ede25311c7db0e0d888889 100644 (file)
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1722,6 +1722,18 @@ void DwarfDebug::emitDebugLocValue(ByteStreamer &Streamer,
       Streamer.EmitInt8(dwarf::DW_OP_constu, "DW_OP_constu");
       Streamer.EmitULEB128(Value.getInt());
     }
+    // The proper way to describe a constant value is 
+    // DW_OP_constu <const>, DW_OP_stack_value. 
+    // Unfortunately, DW_OP_stack_value was not available until DWARF-4,
+    // so we will continue to generate DW_OP_constu <const> for DWARF-2
+    // and DWARF-3. Technically, this is incorrect since DW_OP_const <const>
+    // actually describes a value at a constant addess, not a constant value. 
+    // However, in the past there was no better way  to describe a constant 
+    // value, so the producers and consumers started to rely on heuristics 
+    // to disambiguate the value vs. location status of the expression. 
+    // See PR21176 for more details.
+    if (getDwarfVersion() >= 4)
+      Streamer.EmitInt8(dwarf::DW_OP_stack_value, "DW_OP_stack_value");
   } else if (Value.isLocation()) {
     MachineLocation Loc = Value.getLoc();
     DIExpression Expr = Value.getExpression();

diff --git a/test/DebugInfo/incorrect-variable-debugloc1.ll b/test/DebugInfo/incorrect-variable-debugloc1.ll
new file mode 100644 (file)
index 0000000..85b9a91
--- /dev/null
+++ b/test/DebugInfo/incorrect-variable-debugloc1.ll
@@ -0,0 +1,77 @@
+; REQUIRES: object-emission
+; This test is failing for powerpc64, because a location list for the
+; variable 'c' is not generated at all. Temporary marking this test as XFAIL 
+; for powerpc, until PR21881 is fixed.
+; XFAIL: powerpc64
+
+; RUN: %llc_dwarf -O2  -dwarf-version 2 -filetype=obj < %s | llvm-dwarfdump - | FileCheck %s  --check-prefix=DWARF23
+; RUN: %llc_dwarf -O2  -dwarf-version 3 -filetype=obj < %s | llvm-dwarfdump - | FileCheck %s  --check-prefix=DWARF23
+; RUN: %llc_dwarf -O2  -dwarf-version 4 -filetype=obj < %s | llvm-dwarfdump - | FileCheck %s  --check-prefix=DWARF4
+
+; This is a test for PR21176.
+; DW_OP_const <const> doesn't describe a constant value, but a value at a constant address. 
+; The proper way to describe a constant value is DW_OP_constu <const>, DW_OP_stack_value.
+
+; Generated with clang -S -emit-llvm -g -O2 test.cpp
+
+; extern int func();
+; 
+; int main()
+; {
+;   volatile int c = 13;
+;   c = func();
+;   return c;
+; }
+
+; DWARF23: Location description: 10 0d {{$}}
+; DWARF4: Location description: 10 0d 9f
+
+; Function Attrs: uwtable
+define i32 @main() #0 {
+entry:
+  %c = alloca i32, align 4
+  tail call void @llvm.dbg.value(metadata !15, i64 0, metadata !10, metadata !16), !dbg !17
+  store volatile i32 13, i32* %c, align 4, !dbg !18
+  %call = tail call i32 @_Z4funcv(), !dbg !19
+  tail call void @llvm.dbg.value(metadata !{i32 %call}, i64 0, metadata !10, metadata !16), !dbg !17
+  store volatile i32 %call, i32* %c, align 4, !dbg !19
+  tail call void @llvm.dbg.value(metadata !{i32* %c}, i64 0, metadata !10, metadata !16), !dbg !17
+  %c.0.c.0. = load volatile i32* %c, align 4, !dbg !20
+  ret i32 %c.0.c.0., !dbg !20
+}
+
+declare i32 @_Z4funcv() #1
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #2
+
+attributes #0 = { uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { nounwind readnone }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!12, !13}
+!llvm.ident = !{!14}
+
+!0 = metadata !{metadata !"0x11\004\00clang version 3.6.0 (trunk 223522)\001\00\000\00\001", metadata !1, metadata !2, metadata !2, metadata !3, metadata !2, metadata !2} ; [ DW_TAG_compile_unit ] [/home/kromanova/ngh/ToT_latest/llvm/test/DebugInfo/test.cpp] [DW_LANG_C_plus_plus]
+!1 = metadata !{metadata !"test.cpp", metadata !"/home/kromanova/ngh/ToT_latest/llvm/test/DebugInfo"}
+!2 = metadata !{}
+!3 = metadata !{metadata !4}
+!4 = metadata !{metadata !"0x2e\00main\00main\00\003\000\001\000\000\00256\001\004", metadata !1, metadata !5, metadata !6, null, i32 ()* @main, null, null, metadata !9} ; [ DW_TAG_subprogram ] [line 3] [def] [scope 4] [main]
+!5 = metadata !{metadata !"0x29", metadata !1}    ; [ DW_TAG_file_type ] [/home/kromanova/ngh/ToT_latest/llvm/test/DebugInfo/test.cpp]
+!6 = metadata !{metadata !"0x15\00\000\000\000\000\000\000", null, null, null, metadata !7, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!7 = metadata !{metadata !8}
+!8 = metadata !{metadata !"0x24\00int\000\0032\0032\000\000\005", null, null} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
+!9 = metadata !{metadata !10}
+!10 = metadata !{metadata !"0x100\00c\005\000", metadata !4, metadata !5, metadata !11} ; [ DW_TAG_auto_variable ] [c] [line 5]
+!11 = metadata !{metadata !"0x35\00\000\000\000\000\000", null, null, metadata !8} ; [ DW_TAG_volatile_type ] [line 0, size 0, align 0, offset 0] [from int]
+!12 = metadata !{i32 2, metadata !"Dwarf Version", i32 2}
+!13 = metadata !{i32 2, metadata !"Debug Info Version", i32 2}
+!14 = metadata !{metadata !"clang version 3.6.0 (trunk 223522)"}
+!15 = metadata !{i32 13}
+!16 = metadata !{metadata !"0x102"}               ; [ DW_TAG_expression ]
+!17 = metadata !{i32 5, i32 16, metadata !4, null}
+!18 = metadata !{i32 5, i32 3, metadata !4, null}
+!19 = metadata !{i32 6, i32 7, metadata !4, null}
+!20 = metadata !{i32 7, i32 3, metadata !4, null}
+