[DebugInfo][LSR] Fix assertion failure salvaging IV with offset > 64 bits wide

[OCHyams]

Fixes #110494

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Orlando Cazalet-Hyams (OCHyams)

Changes

Fixes #110494

---

Full diff: https://github.com/llvm/llvm-project/pull/110979.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp (+2)
• (added) llvm/test/Transforms/LoopStrengthReduce/debuginfo-scev-salvage-large-width.ll (+40)

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 3ca3818938fd26..1ad63cb5bf4563 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -6869,6 +6869,8 @@ static bool SalvageDVI(llvm::Loop *L, ScalarEvolution &SE,
             SE.computeConstantDifference(DVIRec.SCEVs[i], SCEVInductionVar)) {
       if (Offset->getSignificantBits() <= 64)
         SalvageExpr->createOffsetExpr(Offset->getSExtValue(), LSRInductionVar);
+      else
+        return false;
     } else if (!SalvageExpr->createIterCountExpr(DVIRec.SCEVs[i], IterCountExpr,
                                                  SE))
       return false;
diff --git a/llvm/test/Transforms/LoopStrengthReduce/debuginfo-scev-salvage-large-width.ll b/llvm/test/Transforms/LoopStrengthReduce/debuginfo-scev-salvage-large-width.ll
new file mode 100644
index 00000000000000..dcd17cae59f4d7
--- /dev/null
+++ b/llvm/test/Transforms/LoopStrengthReduce/debuginfo-scev-salvage-large-width.ll
@@ -0,0 +1,40 @@
+; RUN: opt -S -loop-reduce %s | FileCheck %s
+
+;; We (currently?) can't salvage an IV if the offset is wider than 64 bits.
+;; Check we poison it instead.
+
+; CHECK: #dbg_value(i[[#]] poison, ![[#]], !DIExpression(), ![[#]])
+
+define i16 @main() {
+entry:
+  br label %for.cond29
+
+for.cond29:                                       ; preds = %for.body32, %entry
+  %il_1000.0 = phi i128 [ 0, %entry ], [ %inc72, %for.body32 ]
+  %l_995.0 = phi i128 [ 4704496199548239085565, %entry ], [ %inc70, %for.body32 ]
+    #dbg_value(i128 %l_995.0, !4, !DIExpression(), !9)
+  %cmp30 = icmp slt i128 %il_1000.0, 0
+  br i1 %cmp30, label %for.body32, label %for.cond.cleanup31
+
+for.cond.cleanup31:                               ; preds = %for.cond29
+  ret i16 0
+
+for.body32:                                       ; preds = %for.cond29
+  %inc70 = add i128 %l_995.0, 1
+  %inc72 = add i128 %il_1000.0, 1
+  br label %for.cond29
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, retainedTypes: !2, globals: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "foo.c", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !DILocalVariable(name: "l_995", scope: !5, file: !1, line: 414, type: !7)
+!5 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 397, type: !6, scopeLine: 398, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!6 = !DISubroutineType(types: !2)
+!7 = !DIDerivedType(tag: DW_TAG_typedef, name: "__uint128_t", file: !1, baseType: !8)
+!8 = !DIBasicType(name: "unsigned __int128", size: 128, encoding: DW_ATE_unsigned)
+!9 = !DILocation(line: 0, scope: !5)

[jmorse]

LGTM

[mikaelholmen]

Thanks! I've verified that this patch solves the problem I saw.