[Assignment Tracking] Fix assertion in AssignmentTrackingPass::runOnFunction

The assertion exists to ensure all variables passed into `trackAssignments` end
up with dbg.assigns associated with their backing allocas. The assertion
compared the passed-in and tracked variables using `DebugVariable`, which
includes the fragment as part of the variable identity.

It is possible for the backing alloca to be smaller than a variable (see test
case). In this case the input variable `(Var X, no fragment, no InlinedAt)`
isn't equal to the dbg.assign variable `(Var X, some fragment, no
InlinedAt)`. To cover this case the assertion now ignores fragments through the
use of `DebugVariableAggregate`.

Reviewed By: jmorse

Differential Revision: https://reviews.llvm.org/D148100

Author: OCHyams

llvm/lib/IR/DebugInfo.cpp

@@ -2025,10 +2025,14 @@ bool AssignmentTrackingPass::runOnFunction(Function &F) {
     (void)Markers;
     for (DbgDeclareInst *DDI : P.second) {
       // Assert that the alloca that DDI uses is now linked to a dbg.assign
-      // describing the same variable (i.e. check that this dbg.declare
-      // has been replaced by a dbg.assign).
+      // describing the same variable (i.e. check that this dbg.declare has
+      // been replaced by a dbg.assign). Use DebugVariableAggregate to Discard
+      // the fragment part because trackAssignments may alter the
+      // fragment. e.g. if the alloca is smaller than the variable, then
+      // trackAssignments will create an alloca-sized fragment for the
+      // dbg.assign.
       assert(llvm::any_of(Markers, [DDI](DbgAssignIntrinsic *DAI) {
-        return DebugVariable(DAI) == DebugVariable(DDI);
+        return DebugVariableAggregate(DAI) == DebugVariableAggregate(DDI);
       }));
       // Delete DDI because the variable location is now tracked using
       // assignment tracking.

llvm/test/DebugInfo/Generic/assignment-tracking/declare-to-assign/long-double-x87.ll

@@ -0,0 +1,39 @@
+; RUN: opt %s -S -passes=declare-to-assign -o - | FileCheck %s
+
+;; Generated from this C++:
+;; long double get();
+;; void fun() {
+;;   long double f;
+;; }
+
+;; Check a variable that is larger (128 bits according to !15) than its backing
+;; alloca (80 bits) can be represented with assignment tracking. Create a
+;; fragment for the dbg.assign for bits 0-80.
+
+; CHECK: llvm.dbg.assign(metadata i1 undef, metadata ![[#]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 80), metadata ![[#]], metadata ptr %f, metadata !DIExpression())
+
+define dso_local void @_Z3funv() #0 !dbg !10 {
+entry:
+  %f = alloca x86_fp80, align 16
+  call void @llvm.dbg.declare(metadata ptr %f, metadata !14, metadata !DIExpression()), !dbg !16
+  ret void
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 17.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{!"clang version 17.0.0"}
+!10 = distinct !DISubprogram(name: "fun", linkageName: "_Z3funv", scope: !1, file: !1, line: 2, type: !11, scopeLine: 2, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !13)
+!11 = !DISubroutineType(types: !12)
+!12 = !{null}
+!13 = !{}
+!14 = !DILocalVariable(name: "f", scope: !10, file: !1, line: 3, type: !15)
+!15 = !DIBasicType(name: "long double", size: 128, encoding: DW_ATE_float)
+!16 = !DILocation(line: 3, column: 15, scope: !10)