[llvm] [llvm-dwarfdump][LineCov 1/3] Add variable coverage metrics (PR #169646)

[Stephen Tozer via llvm-commits]

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@@ -0,0 +1,134 @@
+; The source code of the test case:
+; extern void fn3(int *);
+; extern void fn2 (int);
+; __attribute__((noinline))
+; void
+; fn1 (int x, int y)
+; {
+;   int u = x + y;
+;   if (x > 1)
+;     u += 1;
+;   else
+;     u += 2;
+;   if (y > 4)
+;     u += x;
+;   int a = 7;
+;   fn2 (a);
+;   u --;
+; }
+
+; __attribute__((noinline))
+; int f()
+; {
+;   int l, k;
+;   fn3(&l);
+;   fn3(&k);
+;   fn1 (l, k);
+;   return 0;
+; }
+
+; ModuleID = 'test.c'
+source_filename = "test.c"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noinline nounwind uwtable
+define dso_local void @fn1(i32 noundef %0, i32 noundef %1) local_unnamed_addr !dbg !9 {
+  call void @llvm.dbg.value(metadata i32 %0, metadata !14, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.value(metadata i32 %1, metadata !15, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.value(metadata !DIArgList(i32 %0, i32 %1), metadata !16, metadata !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_stack_value)), !dbg !18
+  call void @llvm.dbg.value(metadata i32 undef, metadata !16, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.value(metadata i32 undef, metadata !16, metadata !DIExpression()), !dbg !18
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SLTozer wrote:

I think this file was probably generated by an older compiler version - 2 recommended changes for this and the other test file are:
- Use `metadata i32 poison` instead of `metadata i32 undef`; we try to avoid adding new instances of `undef` except for where there is actual undefined behaviour (and dead debug values are emitted with poison now rather than undef).
- Use debug value records instead of intrinsics - see [here](https://llvm.org/docs/SourceLevelDebugging.html#debug-records) for the docs.

https://github.com/llvm/llvm-project/pull/169646