[Assignment Tracking] Allow salvaging with variadic expressions [4/x]

[Orlando]

Summary

Allow the value-component of a dbg.assign to be salvaged using a variadic DIExpression

llvm/lib/Transforms/Utils/Local.cpp

for (auto *DII : DbgUsers) {
     // DbgUsers, or none of them.
     if (!Op0)
       break;
 
     DII->replaceVariableLocationOp(&I, Op0);
     bool IsValidSalvageExpr = SalvagedExpr->getNumElements() <= MaxExpressionSize;
     if (AdditionalValues.empty() && IsValidSalvageExpr) {
       DII->setExpression(SalvagedExpr);
-    } else if (isa<DbgValueInst>(DII) && !isa<DbgAssignIntrinsic>(DII) &&
-               IsValidSalvageExpr &&
+    } else if (isa<DbgValueInst>(DII) && IsValidSalvageExpr &&
                DII->getNumVariableLocationOps() + AdditionalValues.size() <=
                    MaxDebugArgs) {
       DII->addVariableLocationOps(AdditionalValues, SalvagedExpr);
     } else {
       // Do not salvage using DIArgList for dbg.declare, as it is not currently
-      // supported in those instructions. Do not salvage using DIArgList for
-      // dbg.assign yet. FIXME: support this.
-      // Also do not salvage if the resulting DIArgList would contain an
-      // unreasonably large number of values.
+      // supported in those instructions. Also do not salvage if the resulting
+      // DIArgList would contain an unreasonably large number of values.
       DII->setKillLocation();
     }
     LLVM_DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');
     Salvaged = true;
   }
 
   if (Salvaged)
     return;

llvm/test/DebugInfo/Generic/assignment-tracking/salvage-value.ll

 ; RUN: opt %s -S -o - -passes=instcombine \
 ; RUN: | FileCheck %s --implicit-check-not="call void @llvm.dbg"
 
 ;; Hand-written (the debug info doesn't necessarily make sense and isn't fully
 ;; formed). Test salvaging a dbg.assign value and address. Checks and comments
 ;; are inline.
 
 define dso_local void @fun(i32  %x, i32 %y, ptr %p) !dbg !7 {
 entry:
   %add = add nsw i32 %x, 1, !dbg !22
   call void @llvm.dbg.assign(metadata i32 %add, metadata !14, metadata !DIExpression(), metadata !28, metadata ptr %p, metadata !DIExpression()), !dbg !16
 ;; %add is salvaged.
 ; CHECK: call void @llvm.dbg.assign(metadata i32 %x,{{.+}}metadata !DIExpression(DW_OP_plus_uconst, 1, DW_OP_stack_value),{{.+}}, metadata ptr %p, metadata !DIExpression())
 
  %add1 = add nsw i32 %x, %y, !dbg !29
  call void @llvm.dbg.assign(metadata i32 %add1, metadata !32, metadata !DIExpression(), metadata !31, metadata ptr %p, metadata !DIExpression()), !dbg !16
-;; %add1 is not salvaged as it requires two values and DIArgList is
-;; not (yet) supported for dbg.assigns.
-; CHECK-NEXT: call void @llvm.dbg.assign(metadata i32 poison,{{.+}}, metadata !DIExpression(),{{.+}}, metadata ptr %p, metadata !DIExpression())
+;; %add1 is salvaged using a variadic expression.
+; CHECK-NEXT: call void @llvm.dbg.assign(metadata !DIArgList(i32 %x, i32 %y), metadata ![[#]], metadata !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_stack_value), metadata ![[#]], metadata ptr %p, metadata !DIExpression())
 
   %arrayidx0 = getelementptr inbounds i32, ptr %p, i32 0
   call void @llvm.dbg.assign(metadata i32 %x, metadata !14, metadata !DIExpression(), metadata !17, metadata ptr %arrayidx0, metadata !DIExpression()), !dbg !16
 ;; %arrayidx0 is salvaged (zero offset, so the gep is just replaced with %p).
 ; CHECK-NEXT: call void @llvm.dbg.assign(metadata i32 %x,{{.+}}, metadata !DIExpression(),{{.+}}, metadata ptr %p, metadata !DIExpression())
 
   %arrayidx1 = getelementptr inbounds i32, ptr %p, i32 1
   call void @llvm.dbg.assign(metadata i32 %x, metadata !33, metadata !DIExpression(), metadata !18, metadata ptr %arrayidx1, metadata !DIExpression()), !dbg !16