[llvm] [DebugInfo] Add DW_OP_LLVM_extract_bits (PR #93990)

[John Brawn via llvm-commits]

================
@@ -0,0 +1,99 @@
+; RUN: llc -mtriple=x86_64-unknown-linux-gnu %s -o %t -filetype=obj
+; RUN: llvm-dwarfdump --debug-info %t | FileCheck %s
+
+%struct.struct_t = type { i8 }
+
+ at g = dso_local global %struct.struct_t zeroinitializer, align 1, !dbg !0
+
+; CHECK-LABEL: DW_TAG_subprogram
+; CHECK: DW_AT_name ("test1")
+; CHECK: DW_TAG_variable
+; CHECK: DW_AT_location (DW_OP_fbreg -1, DW_OP_deref, DW_OP_constu 0x3d, DW_OP_shl, DW_OP_constu 0x3d, DW_OP_shr, DW_OP_stack_value)
+; CHECK: DW_AT_name ("x")
+; CHECK: DW_TAG_variable
+; CHECK: DW_AT_location (DW_OP_fbreg -1, DW_OP_deref, DW_OP_constu 0x39, DW_OP_shl, DW_OP_constu 0x3c, DW_OP_shra, DW_OP_stack_value)
+; CHECK: DW_AT_name ("y")
+
+define i32 @test1() !dbg !13 {
+entry:
+  %0 = alloca %struct.struct_t, align 1
+  tail call void @llvm.dbg.declare(metadata ptr %0, metadata !17, metadata !DIExpression(DW_OP_LLVM_extract_bits, 0, 3, DW_ATE_unsigned)), !dbg !18
+  tail call void @llvm.dbg.declare(metadata ptr %0, metadata !19, metadata !DIExpression(DW_OP_LLVM_extract_bits, 3, 4, DW_ATE_signed)), !dbg !21
+  ret i32 0, !dbg !22
+}
+
+; CHECK-LABEL: DW_TAG_subprogram
+; CHECK: DW_AT_name ("test2")
+; CHECK: DW_TAG_variable
+; CHECK: DW_AT_location (DW_OP_breg0 RAX+0, DW_OP_constu 0xff, DW_OP_and, DW_OP_constu 0x3d, DW_OP_shl, DW_OP_constu 0x3d, DW_OP_shr, DW_OP_stack_value)
+; CHECK: DW_AT_name ("x")
+; CHECK: DW_TAG_variable
+; CHECK: DW_AT_location (DW_OP_breg0 RAX+0, DW_OP_constu 0xff, DW_OP_and, DW_OP_constu 0x39, DW_OP_shl, DW_OP_constu 0x3c, DW_OP_shra, DW_OP_stack_value)
+; CHECK: DW_AT_name ("y")
+
+define i8 @test2() !dbg !23 {
+entry:
+  %0 = load i8, ptr @g, align 1
+  tail call void @llvm.dbg.value(metadata i8 %0, metadata !24, metadata !DIExpression(DW_OP_LLVM_extract_bits, 0, 3, DW_ATE_unsigned)), !dbg !25
+  tail call void @llvm.dbg.value(metadata i8 %0, metadata !26, metadata !DIExpression(DW_OP_LLVM_extract_bits, 3, 4, DW_ATE_signed)), !dbg !27
+  ret i8 %0, !dbg !28
+}
+
+; CHECK-LABEL: DW_TAG_subprogram
+; CHECK: DW_AT_name ("test3")
+; CHECK: DW_TAG_variable
+; CHECK: DW_AT_location (DW_OP_breg0 RAX+0, DW_OP_constu 0x3f, DW_OP_shr, DW_OP_stack_value)
----------------
john-brawn-arm wrote:

It looks like MIR doesn't handle multiple debug values in the same stack location. The MIR generated for test1 (by running DW_OP_LLVM_extract_bits.ll through llc with --stop-after=patchable-function) has
```
stack:
  - { id: 0, name: '', type: default, offset: -9, size: 1, alignment: 1,
      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
      debug-info-variable: '!17!19', debug-info-expression: '!DIExpression(DW_OP_LLVM_extract_bits, 0, 3, DW_ATE_unsigned)!DIExpression(DW_OP_LLVM_extract_bits, 3, 4, DW_ATE_signed)',
      debug-info-location: '!18!21' }
```
which llc then gives an error for on reading it:
```
error: tmp.mir:130:32: expected end of string after the metadata node
      debug-info-variable: '!17!19', debug-info-expression: '!DIExpression(DW_OP_LLVM_extract_bits, 0, 3, DW_ATE_unsigned)!DIExpression(DW_OP_LLVM_extract_bits, 3, 4, DW_ATE_signed)',
                               ^
```


https://github.com/llvm/llvm-project/pull/93990