[DebugInfo] Enable variadic debug value salvaging

This patch enables the salvaging of debug values that may be calculated
from more than one SSA value, such as with binary operators that do not
use a constant argument. The actual functionality for this behaviour is
added in a previous commit (c727056), but with the ability to actually
emit the resulting debug values switched off.

The reason for this is that the prior patch has been reverted several
times due to issues discovered downstream, some time after the actual
landing of the patch. The patch in question is rather large and touches
several widely used header files, and all issues discovered are more
related to the handling of variadic debug values as a whole rather than
the details of the patch itself. Therefore, to minimize the build time
impact and risk of conflicts involved in any potential future
revert/reapply of that patch, this significantly smaller patch (that
touches no header files) will instead be used as the capstone to enable
variadic debug value salvaging.

The review linked to this patch is mostly implemented by the previous
commit, c727056, but also contains the changes in this patch.

Differential Revision: https://reviews.llvm.org/D91722

Author: SLTozer

llvm/lib/Transforms/Utils/Local.cpp

@@ -1748,11 +1748,7 @@ void llvm::salvageDebugInfoForDbgValues(
     } else if (isa<DbgValueInst>(DII) &&
                DII->getNumVariableLocationOps() + AdditionalValues.size() <=
                    MaxDebugArgs) {
-      // TODO: Uncomment the line below and delete the two beneath it to enable
-      // salvaging of dbg.values with multiple location operands.
-      // DII->addVariableLocationOps(AdditionalValues, SalvagedExpr);
-      Value *Undef = UndefValue::get(I.getOperand(0)->getType());
-      DII->replaceVariableLocationOp(I.getOperand(0), Undef);
+      DII->addVariableLocationOps(AdditionalValues, SalvagedExpr);
     } else {
       // Do not salvage using DIArgList for dbg.addr/dbg.declare, as it is
       // currently only valid for stack value expressions.

llvm/test/DebugInfo/NVPTX/debug-info.ll

@@ -702,12 +702,12 @@ if.end:                                           ; preds = %if.then, %entry
 ; CHECK-NEXT:	}
 ; CHECK-NEXT:	.section	.debug_info
 ; CHECK-NEXT:	{
-; CHECK-NEXT:.b32 10029                              // Length of Unit
+; CHECK-NEXT:.b32 10034                              // Length of Unit
 ; CHECK-NEXT:.b8 2                                   // DWARF version number
 ; CHECK-NEXT:.b8 0
 ; CHECK-NEXT:.b32 .debug_abbrev                      // Offset Into Abbrev. Section
 ; CHECK-NEXT:.b8 8                                   // Address Size (in bytes)
-; CHECK-NEXT:.b8 1                                   // Abbrev [1] 0xb:0x2726 DW_TAG_compile_unit
+; CHECK-NEXT:.b8 1                                   // Abbrev [1] 0xb:0x272b DW_TAG_compile_unit
 ; CHECK-NEXT:.b8 0                                   // DW_AT_producer
 ; CHECK-NEXT:.b8 4                                   // DW_AT_language
 ; CHECK-NEXT:.b8 0
@@ -8306,7 +8306,7 @@ if.end:                                           ; preds = %if.then, %entry
 ; CHECK-NEXT:.b8 3                                   // DW_AT_decl_line
 ; CHECK-NEXT:.b32 3345                               // DW_AT_type
 ; CHECK-NEXT:.b8 0                                   // End Of Children Mark
-; CHECK-NEXT:.b8 40                                  // Abbrev [40] 0x2671:0xbf DW_TAG_subprogram
+; CHECK-NEXT:.b8 40                                  // Abbrev [40] 0x2671:0xc4 DW_TAG_subprogram
 ; CHECK-NEXT:.b64 Lfunc_begin0                       // DW_AT_low_pc
 ; CHECK-NEXT:.b64 Lfunc_end0                         // DW_AT_high_pc
 ; CHECK-NEXT:.b8 1                                   // DW_AT_frame_base
@@ -8386,7 +8386,7 @@ if.end:                                           ; preds = %if.then, %entry
 ; CHECK-NEXT:.b8 12                                  // DW_AT_call_file
 ; CHECK-NEXT:.b8 6                                   // DW_AT_call_line
 ; CHECK-NEXT:.b8 37                                  // DW_AT_call_column
-; CHECK-NEXT:.b8 43                                  // Abbrev [43] 0x2711:0x1e DW_TAG_inlined_subroutine
+; CHECK-NEXT:.b8 43                                  // Abbrev [43] 0x2711:0x23 DW_TAG_inlined_subroutine
 ; CHECK-NEXT:.b32 9791                               // DW_AT_abstract_origin
 ; CHECK-NEXT:.b64 Ltmp9                              // DW_AT_low_pc
 ; CHECK-NEXT:.b64 Ltmp10                             // DW_AT_high_pc
@@ -8395,6 +8395,8 @@ if.end:                                           ; preds = %if.then, %entry
 ; CHECK-NEXT:.b8 5                                   // DW_AT_call_column
 ; CHECK-NEXT:.b8 44                                  // Abbrev [44] 0x2729:0x5 DW_TAG_formal_parameter
 ; CHECK-NEXT:.b32 9820                               // DW_AT_abstract_origin
+; CHECK-NEXT:.b8 44                                  // Abbrev [44] 0x272e:0x5 DW_TAG_formal_parameter
+; CHECK-NEXT:.b32 9829                               // DW_AT_abstract_origin
 ; CHECK-NEXT:.b8 0                                   // End Of Children Mark
 ; CHECK-NEXT:.b8 0                                   // End Of Children Mark
 ; CHECK-NEXT:.b8 0                                   // End Of Children Mark

llvm/test/DebugInfo/salvage-gep.ll

@@ -1,4 +1,3 @@
-; XFAIL: *
 ; RUN: opt %s -dce -S | FileCheck %s
 
 ; Tests the salvaging of GEP instructions, specifically struct indexing and

llvm/test/DebugInfo/salvage-nonconst-binop.ll

@@ -1,4 +1,3 @@
-; XFAIL: *
 ; RUN: opt %s -dce -S | FileCheck %s
 
 ; Tests the salvaging of binary operators that use more than one non-constant