[Assignment Tracking] Ignore stores to a negative offset from an alloca

Fixes crash reported in llvm.org/PR62838.

Reviewed By: jryans

Differential Revision: https://reviews.llvm.org/D151326

Author: OCHyams

llvm/lib/IR/DebugInfo.cpp

@@ -1915,7 +1915,8 @@ bool at::calculateFragmentIntersect(
 }
 
 /// Collect constant properies (base, size, offset) of \p StoreDest.
-/// Return std::nullopt if any properties are not constants.
+/// Return std::nullopt if any properties are not constants or the
+/// offset from the base pointer is negative.
 static std::optional<AssignmentInfo>
 getAssignmentInfoImpl(const DataLayout &DL, const Value *StoreDest,
                       TypeSize SizeInBits) {
@@ -1924,6 +1925,10 @@ getAssignmentInfoImpl(const DataLayout &DL, const Value *StoreDest,
   APInt GEPOffset(DL.getIndexTypeSizeInBits(StoreDest->getType()), 0);
   const Value *Base = StoreDest->stripAndAccumulateConstantOffsets(
       DL, GEPOffset, /*AllowNonInbounds*/ true);
+
+  if (GEPOffset.isNegative())
+    return std::nullopt;
+
   uint64_t OffsetInBytes = GEPOffset.getLimitedValue();
   // Check for overflow.
   if (OffsetInBytes == UINT64_MAX)

llvm/test/DebugInfo/assignment-tracking/X86/negative-offset.ll

@@ -0,0 +1,91 @@
+; RUN: llc %s -stop-after=finalize-isel -o - | FileCheck %s --implicit-check-not=DBG_VALUE
+
+;; Check stores to an address computed as a negative offset from an alloca are
+;; ignored by the assignment tracking analysis. For this example that should
+;; result in no DBG_VALUEs in the while.body.lr.ph branch.
+;;
+;; See llvm.org/PR62838 for more info.
+;;
+;; $ clang test.c -O1 -g
+;; $ cat tes.c
+;; void a(int *p);
+;; __attribute__((nodebug)) int b;
+;;
+;; int main() {
+;;   int c[1];
+;;   __attribute__((nodebug)) int d = -1;
+;;
+;;   while (b) {
+;;     c[0] = 0;
+;;     c[d] = 0;
+;;   }
+;;   a(c);
+;;   return 0;
+;; }
+
+; CHECK: bb.0.entry:
+; CHECK-NEXT: successors
+; CHECK-NEXT: {{^ *$}}
+; CHECK-NEXT: DBG_VALUE %stack.0.c, $noreg, ![[#]], !DIExpression(DW_OP_deref)
+
+; CHECK:  bb.2.while.body:
+; CHECK-NEXT: successors
+; CHECK-NEXT: {{^ *$}}
+; CHECK-NEXT: DBG_VALUE 0, $noreg, ![[#]], !DIExpression()
+
+target triple = "x86_64-unknown-linux-gnu"
+
+@b = dso_local local_unnamed_addr global i32 0, align 4
+
+define dso_local i32 @main() local_unnamed_addr #0 !dbg !10 {
+entry:
+  %c = alloca [1 x i32], align 4, !DIAssignID !19
+  call void @llvm.dbg.assign(metadata i1 undef, metadata !15, metadata !DIExpression(), metadata !19, metadata ptr %c, metadata !DIExpression()), !dbg !20
+  %0 = load i32, ptr @b, align 4
+  %tobool.not = icmp eq i32 %0, 0
+  br i1 %tobool.not, label %while.end, label %while.body.lr.ph
+
+while.body.lr.ph:                                 ; preds = %entry
+  %arrayidx1 = getelementptr inbounds [1 x i32], ptr %c, i64 0, i64 -1
+  store i32 0, ptr %arrayidx1, align 4
+  br label %while.body
+
+while.body:                                       ; preds = %while.body, %while.body.lr.ph
+  call void @llvm.dbg.assign(metadata i32 0, metadata !15, metadata !DIExpression(), metadata !28, metadata ptr %c, metadata !DIExpression()), !dbg !20
+  br label %while.body
+
+while.end:                                        ; preds = %entry
+  call void @a(ptr noundef nonnull %c)
+  ret i32 0
+}
+
+declare !dbg !31 void @a(ptr noundef) local_unnamed_addr #2
+declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata) #3
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !8}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 17.0.0)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.c", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !{i32 7, !"debug-info-assignment-tracking", i1 true}
+!9 = !{!"clang version 17.0.0"}
+!10 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 4, type: !11, scopeLine: 4, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !14)
+!11 = !DISubroutineType(types: !12)
+!12 = !{!13}
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !{!15}
+!15 = !DILocalVariable(name: "c", scope: !10, file: !1, line: 5, type: !16)
+!16 = !DICompositeType(tag: DW_TAG_array_type, baseType: !13, size: 32, elements: !17)
+!17 = !{!18}
+!18 = !DISubrange(count: 1)
+!19 = distinct !DIAssignID()
+!20 = !DILocation(line: 0, scope: !10)
+!28 = distinct !DIAssignID()
+!31 = !DISubprogram(name: "a", scope: !1, file: !1, line: 1, type: !32, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !35)
+!32 = !DISubroutineType(types: !33)
+!33 = !{null, !34}
+!34 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64)
+!35 = !{}