[llvm-bugs] [Bug 44118] New: Incorrect DW_AT_location attribute for call site parameter entry

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44118

            Bug ID: 44118
           Summary: Incorrect DW_AT_location attribute for call site
                    parameter entry
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: DebugInfo
          Assignee: unassignedbugs at nondot.org
          Reporter: david.stenberg at ericsson.com
                CC: jdevlieghere at apple.com, keith.walker at arm.com,
                    llvm-bugs at lists.llvm.org,
                    paul_robinson at playstation.sony.com

Reproduced on 3889ff82bf4057ead22dad91a89384ac20ebd557.

Compiling the following file:

  extern void callee(int, int);
  extern int a;

  int caller(int e, long c) {
    callee(c, a);
    return e;
  }

using:

  clang --target=aarch64 -O1 -g -Xclang -femit-debug-entry-values -c location.c

yields the following call site parameter entry:

  0x00000087:       DW_TAG_GNU_call_site_parameter
                    DW_AT_location      (DW_OP_reg8 W8)
                    DW_AT_GNU_call_site_value  
(DW_OP_GNU_entry_value(DW_OP_reg1 W1))

As seen, the DW_AT_location attribute specifies W8, but as this is a call site
entry for the first parameter, it should be W0.

In this case the value is described by a chain of instructions:

  bb.0.entry:
    liveins: $w0, $x1, $lr, $x19
    [...]
    $x8 = ORRXrs $xzr, killed $x1, 0
    [...]
    $w0 = ORRWrs $wzr, killed $w8, 0, implicit $x8, debug-location !26
    BL @callee, csr_aarch64_aapcs

At a quick glance, it seems that this code in collectCallSiteParameters() only
resolves one step of the chain, resulting in the location becoming incorrect:

  // Emit the call site parameter's value as an entry value.
  if (ShouldTryEmitEntryVals) {
    // Create an expression where the register's entry value is used.
    DIExpression *EntryExpr = DIExpression::get(
        MF->getFunction().getContext(), {dwarf::DW_OP_LLVM_entry_value, 1}); 
    for (auto RegEntry : ForwardedRegWorklist) {
      unsigned FwdReg = RegEntry;
      auto EntryValReg = RegsForEntryValues.find(RegEntry);
        if (EntryValReg != RegsForEntryValues.end())
          FwdReg = EntryValReg->second;

      DbgValueLoc DbgLocVal(EntryExpr, MachineLocation(RegEntry));
      DbgCallSiteParam CSParm(FwdReg, DbgLocVal);                               
      Params.push_back(CSParm);
      ++NumCSParams;
    }    
  }

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