DwarfDebug: Support floating point constants in location lists.

This patch closes a gap in the DWARF backend that caused LLVM to drop
debug info for floating point variables that were constant for part of
their scope. Floating point constants are emitted as one or more
DW_OP_constu joined via DW_OP_piece.

This fixes a regression caught by the LLDB testsuite that I introduced
in r262247 when we stopped blindly expanding the range of singular
DBG_VALUEs to span the entire scope and started to emit location lists
with accurate ranges instead.

Also deletes a now-impossible testcase (debug-loc-empty-entries).

<rdar://problem/25448338>

llvm-svn: 265760

2 files changed, 86 insertions, 66 deletions

diff --git a/llvm/test/DebugInfo/X86/debug-loc-empty-entries.ll b/llvm/test/DebugInfo/X86/debug-loc-empty-entries.ll
deleted file mode 100644
index c26d8aea2d1..00000000000
--- a/llvm/test/DebugInfo/X86/debug-loc-empty-entries.ll
+++ /dev/null
@@ -1,66 +0,0 @@
-; RUN: llc -mtriple=x86_64-apple-macosx <%s | FileCheck %s
-; Test that we don't generate empty .debug_loc entries.  Originally, there were
-; two empty .debug_loc entries for 'a' in an otherwise empty .debug_loc list.
-;
-; CHECK:      .section __DWARF,__debug_loc,regular,debug
-; CHECK-NEXT: Lsection_debug_loc:
-; CHECK-NEXT: .section __DWARF,__debug_abbrev,regular,debug
-;
-; Test that the variable stuck around.
-; CHECK:      .section __DWARF,__debug_info,regular,debug
-; CHECK:      DW_TAG_variable
-; CHECK-NOT:  DW_AT_location
-
-; Generated using clang -cc1 with the following args:
-;
-;   -triple x86_64-apple-macosx -emit-llvm -gdwarf-4 -O1
-;
-; From this testcase:
-;
-;;   void fn1() {
-;;     float a = 1;
-;;     for (;;)
-;;       a = 0;
-;;   }
-
-; Function Attrs: noreturn nounwind readnone
-define void @_Z3fn1v() #0 !dbg !4 {
-entry:
-  tail call void @llvm.dbg.value(metadata float 1.000000e+00, i64 0, metadata !9, metadata !14), !dbg !15
-  br label %for.cond, !dbg !16
-
-for.cond:                                         ; preds = %for.cond, %entry
-  tail call void @llvm.dbg.value(metadata float 0.000000e+00, i64 0, metadata !9, metadata !14), !dbg !15
-  br label %for.cond, !dbg !17
-}
-
-; Function Attrs: nounwind readnone
-declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #1
-
-attributes #0 = { noreturn nounwind readnone "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-realign-stack" "stack-protector-buffer-size"="8" "target-features"="+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
-attributes #1 = { nounwind readnone }
-
-!llvm.dbg.cu = !{!0}
-!llvm.module.flags = !{!11, !12}
-!llvm.ident = !{!13}
-
-!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 3.7.0 (trunk 238517) (llvm/trunk 238524)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !2, subprograms: !3, globals: !2, imports: !2)
-!1 = !DIFile(filename: "<stdin>", directory: "/Users/dexonsmith/data/llvm/bootstrap/play/delta2/testcase")
-!2 = !{}
-!3 = !{!4}
-!4 = distinct !DISubprogram(name: "fn1", linkageName: "_Z3fn1v", scope: !5, file: !5, line: 1, type: !6, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, variables: !8)
-!5 = !DIFile(filename: "t.cpp", directory: "/Users/dexonsmith/data/llvm/bootstrap/play/delta2/testcase")
-!6 = !DISubroutineType(types: !7)
-!7 = !{null}
-!8 = !{!9}
-!9 = !DILocalVariable(name: "a", scope: !4, file: !5, line: 2, type: !10)
-!10 = !DIBasicType(name: "float", size: 32, align: 32, encoding: DW_ATE_float)
-!11 = !{i32 2, !"Dwarf Version", i32 4}
-!12 = !{i32 2, !"Debug Info Version", i32 3}
-!13 = !{!"clang version 3.7.0 (trunk 238517) (llvm/trunk 238524)"}
-!14 = !DIExpression()
-!15 = !DILocation(line: 2, scope: !4)
-!16 = !DILocation(line: 3, scope: !4)
-!17 = !DILocation(line: 3, scope: !18)
-!18 = distinct !DILexicalBlock(scope: !19, file: !5, line: 3)
-!19 = distinct !DILexicalBlock(scope: !4, file: !5, line: 3)
diff --git a/llvm/test/DebugInfo/X86/float_const_loclist.ll b/llvm/test/DebugInfo/X86/float_const_loclist.ll
new file mode 100644
index 00000000000..eb531178d21
--- /dev/null
+++ b/llvm/test/DebugInfo/X86/float_const_loclist.ll
@@ -0,0 +1,86 @@
+; RUN: llc %s -stop-after=livedebugvalues -o %t 2>&1 | FileCheck --check-prefix=SANITY %s
+; RUN: llc < %s -filetype=obj | llvm-dwarfdump - | FileCheck %s
+; Test debug_loc support for floating point constants.
+;
+; Created from clang -O1:
+;   void barrier();
+;   void foo() {
+;     float f;
+;     long double ld;
+;     barrier();
+;     f = 3.14;
+;     ld = 3.14;
+;     barrier();
+;   }
+;
+; SANITY: CALL{{.*}} @barrier
+; SANITY: DBG_VALUE x86_fp80 0xK4000C8F5C28F5C28F800
+; SANITY: DBG_VALUE float 0x40091EB860000000
+; SANITY: TAILJMP{{.*}} @barrier
+;
+; CHECK: .debug_info contents:
+; CHECK: DW_TAG_variable
+; CHECK-NEXT:  DW_AT_location {{.*}} (0x00000000)
+; CHECK-NEXT:  DW_AT_name {{.*}}"ld"
+; CHECK: DW_TAG_variable
+; CHECK-NEXT:  DW_AT_location {{.*}} (0x00000031)
+; CHECK-NEXT:  DW_AT_name {{.*}}"f"
+;
+; CHECK: .debug_loc contents:
+; CHECK: 0x00000000: Beginning address offset: [[START:.*]]
+; CHECK:                Ending address offset: [[END:.*]]
+; CHECK:                 Location description: 10 80 f0 a3 e1 05 93 08 10 80 80 01 9d 10 40
+;                        constu ..., piece 8, constu ..., bit-piece 16 64
+; CHECK: 0x00000031: Beginning address offset: [[START]]
+; CHECK:                Ending address offset: [[END]]
+; CHECK:                 Location description: 10 c3 eb a3 82 04
+;                                              constu ...
+source_filename = "test.c"
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+; Function Attrs: nounwind ssp uwtable
+define void @foo() #0 !dbg !4 {
+entry:
+  tail call void (...) @barrier() #3, !dbg !16
+  tail call void @llvm.dbg.value(metadata float 0x40091EB860000000, i64 0, metadata !8, metadata !17), !dbg !18
+  tail call void @llvm.dbg.value(metadata x86_fp80 0xK4000C8F5C28F5C28F800, i64 0, metadata !10, metadata !17), !dbg !19
+  tail call void (...) @barrier() #3, !dbg !20
+  ret void, !dbg !21
+}
+
+declare void @barrier(...)
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #2
+
+attributes #0 = { nounwind ssp uwtable }
+attributes #2 = { nounwind readnone }
+attributes #3 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!12, !13, !14}
+!llvm.ident = !{!15}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.9.0 (trunk 265328) (llvm/trunk 265330)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, subprograms: !3)
+!1 = !DIFile(filename: "test.c", directory: "/Volumes/Data/radar/25448338")
+!2 = !{}
+!3 = !{!4}
+!4 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, type: !5, isLocal: false, isDefinition: true, scopeLine: 4, isOptimized: true, variables: !7)
+!5 = !DISubroutineType(types: !6)
+!6 = !{null}
+!7 = !{!8, !10}
+!8 = !DILocalVariable(name: "f", scope: !4, file: !1, line: 5, type: !9)
+!9 = !DIBasicType(name: "float", size: 32, align: 32, encoding: DW_ATE_float)
+!10 = !DILocalVariable(name: "ld", scope: !4, file: !1, line: 6, type: !11)
+!11 = !DIBasicType(name: "long double", size: 128, align: 128, encoding: DW_ATE_float)
+!12 = !{i32 2, !"Dwarf Version", i32 2}
+!13 = !{i32 2, !"Debug Info Version", i32 3}
+!14 = !{i32 1, !"PIC Level", i32 2}
+!15 = !{!"clang version 3.9.0 (trunk 265328) (llvm/trunk 265330)"}
+!16 = !DILocation(line: 7, column: 3, scope: !4)
+!17 = !DIExpression()
+!18 = !DILocation(line: 5, column: 9, scope: !4)
+!19 = !DILocation(line: 6, column: 15, scope: !4)
+!20 = !DILocation(line: 10, column: 3, scope: !4)
+!21 = !DILocation(line: 11, column: 1, scope: !4)