[llvm] [SCEV] Fix cache poisoning from depth-limited truncate expressions (PR #172234)
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Sun Dec 14 14:44:29 PST 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-analysis
Author: Anshil Gandhi (gandhi56)
<details>
<summary>Changes</summary>
Avoid inserting depth-limited unsimplified SCEVTruncateExpr into the UniqueSCEVs cache. Caching these prevents later queries at lower depth from properly simplifying (e.g., trunc(AddRec) -> AddRec).
This fixes an assertion failure in IndVarSimplify where getTruncateExpr on an AddRecExpr returned a cached SCEVTruncateExpr instead of the expected SCEVAddRecExpr.
---
Full diff: https://github.com/llvm/llvm-project/pull/172234.diff
2 Files Affected:
- (modified) llvm/lib/Analysis/ScalarEvolution.cpp (+4-1)
- (added) llvm/test/Transforms/IndVarSimplify/scev-update-loop-opt.ll (+223)
``````````diff
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index e1f90264be7a2..518aba36c5e6d 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -1172,9 +1172,12 @@ const SCEV *ScalarEvolution::getTruncateExpr(const SCEV *Op, Type *Ty,
return getTruncateOrZeroExtend(SZ->getOperand(), Ty, Depth + 1);
if (Depth > MaxCastDepth) {
+ // Avoid caching depth-limited unsimplified results. Later queries at lower
+ // depth should be able to simplify (e.g., truncate of AddRec -> AddRec).
+ // Caching here would return this unsimplified SCEVTruncateExpr for future
+ // queries, preventing proper simplification.
SCEV *S =
new (SCEVAllocator) SCEVTruncateExpr(ID.Intern(SCEVAllocator), Op, Ty);
- UniqueSCEVs.InsertNode(S, IP);
registerUser(S, Op);
return S;
}
diff --git a/llvm/test/Transforms/IndVarSimplify/scev-update-loop-opt.ll b/llvm/test/Transforms/IndVarSimplify/scev-update-loop-opt.ll
new file mode 100644
index 0000000000000..4f994f2458a36
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/scev-update-loop-opt.ll
@@ -0,0 +1,223 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt %s -passes="loop(loop-idiom,indvars,loop-deletion,loop-unroll-full)" -S | FileCheck %s
+; REQUIRES: asserts
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @_ZNK4Test29TestViewOperator_LeftAndRightIiN6Kokkos6SerialELj7EEclEmRi(i32 %conv5, i1 %cmp13, i1 %cmp20, i1 %cmp27, i1 %cmp34, i1 %cmp41) local_unnamed_addr {
+; CHECK-LABEL: define void @_ZNK4Test29TestViewOperator_LeftAndRightIiN6Kokkos6SerialELj7EEclEmRi(
+; CHECK-SAME: i32 [[CONV5:%.*]], i1 [[CMP13:%.*]], i1 [[CMP20:%.*]], i1 [[CMP27:%.*]], i1 [[CMP34:%.*]], i1 [[CMP41:%.*]]) local_unnamed_addr {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[TMP0:%.*]] = add i32 [[CONV5]], 1
+; CHECK-NEXT: [[TMP1:%.*]] = zext i32 [[TMP0]] to i64
+; CHECK-NEXT: br label %[[FOR_COND:.*]]
+; CHECK: [[FOR_COND_LOOPEXIT:.*]]:
+; CHECK-NEXT: br label %[[FOR_COND]]
+; CHECK: [[FOR_COND]]:
+; CHECK-NEXT: [[TMP2:%.*]] = zext i32 [[CONV5]] to i64
+; CHECK-NEXT: br label %[[FOR_COND2:.*]]
+; CHECK: [[FOR_COND2]]:
+; CHECK-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], %[[FOR_COND_CLEANUP14:.*]] ], [ 0, %[[FOR_COND]] ]
+; CHECK-NEXT: [[EXITCOND:%.*]] = icmp ne i64 [[INDVARS_IV]], [[TMP2]]
+; CHECK-NEXT: br i1 [[EXITCOND]], label %[[FOR_COND9_PREHEADER:.*]], label %[[FOR_COND_LOOPEXIT]]
+; CHECK: [[FOR_COND9_PREHEADER]]:
+; CHECK-NEXT: br label %[[FOR_COND9:.*]]
+; CHECK: [[FOR_COND9_LOOPEXIT:.*]]:
+; CHECK-NEXT: br label %[[FOR_COND9]]
+; CHECK: [[FOR_COND9]]:
+; CHECK-NEXT: br i1 [[CMP13]], label %[[FOR_COND16_PREHEADER:.*]], label %[[FOR_COND_CLEANUP14]]
+; CHECK: [[FOR_COND16_PREHEADER]]:
+; CHECK-NEXT: br label %[[FOR_COND16:.*]]
+; CHECK: [[FOR_COND_CLEANUP14]]:
+; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
+; CHECK-NEXT: br label %[[FOR_COND2]]
+; CHECK: [[FOR_COND16_LOOPEXIT:.*]]:
+; CHECK-NEXT: br label %[[FOR_COND16]]
+; CHECK: [[FOR_COND16]]:
+; CHECK-NEXT: br i1 [[CMP20]], label %[[FOR_COND23_PREHEADER:.*]], label %[[FOR_COND9_LOOPEXIT]]
+; CHECK: [[FOR_COND23_PREHEADER]]:
+; CHECK-NEXT: br label %[[FOR_COND23:.*]]
+; CHECK: [[FOR_COND23_LOOPEXIT:.*]]:
+; CHECK-NEXT: br label %[[FOR_COND23]]
+; CHECK: [[FOR_COND23]]:
+; CHECK-NEXT: br i1 [[CMP27]], label %[[FOR_COND30_PREHEADER:.*]], label %[[FOR_COND16_LOOPEXIT]]
+; CHECK: [[FOR_COND30_PREHEADER]]:
+; CHECK-NEXT: br label %[[FOR_COND30:.*]]
+; CHECK: [[FOR_COND30_LOOPEXIT_LOOPEXIT:.*]]:
+; CHECK-NEXT: br label %[[FOR_COND30_LOOPEXIT:.*]]
+; CHECK: [[FOR_COND30_LOOPEXIT]]:
+; CHECK-NEXT: br label %[[FOR_COND30]]
+; CHECK: [[FOR_COND30]]:
+; CHECK-NEXT: br i1 [[CMP34]], label %[[FOR_COND37_PREHEADER:.*]], label %[[FOR_COND23_LOOPEXIT]]
+; CHECK: [[FOR_COND37_PREHEADER]]:
+; CHECK-NEXT: br label %[[FOR_COND37_PEEL_BEGIN:.*]]
+; CHECK: [[FOR_COND37_PEEL_BEGIN]]:
+; CHECK-NEXT: br label %[[FOR_COND37_PEEL:.*]]
+; CHECK: [[FOR_COND37_PEEL]]:
+; CHECK-NEXT: br i1 [[CMP41]], label %[[FOR_BODY43_PEEL:.*]], label %[[FOR_COND30_LOOPEXIT]]
+; CHECK: [[FOR_BODY43_PEEL]]:
+; CHECK-NEXT: [[CONV45_PEEL:%.*]] = zext i32 0 to i64
+; CHECK-NEXT: [[CALL31_I_I_PEEL:%.*]] = load volatile i64, ptr null, align 8
+; CHECK-NEXT: [[MUL79_I_I_PEEL:%.*]] = mul i64 [[CALL31_I_I_PEEL]], [[INDVARS_IV]]
+; CHECK-NEXT: [[DOTIDX1_PEEL:%.*]] = add i64 [[CONV45_PEEL]], [[MUL79_I_I_PEEL]]
+; CHECK-NEXT: [[SUB_PTR_LHS_CAST_PEEL:%.*]] = shl i64 [[DOTIDX1_PEEL]], 2
+; CHECK-NEXT: [[SUB_PTR_DIV_PEEL:%.*]] = ashr exact i64 [[SUB_PTR_LHS_CAST_PEEL]], 1
+; CHECK-NEXT: [[CMP55_PEEL:%.*]] = icmp sgt i64 0, 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[CMP55_PEEL]])
+; CHECK-NEXT: br label %[[FOR_COND37_PEEL_NEXT:.*]]
+; CHECK: [[FOR_COND37_PEEL_NEXT]]:
+; CHECK-NEXT: br label %[[FOR_COND37_PEEL_NEXT1:.*]]
+; CHECK: [[FOR_COND37_PEEL_NEXT1]]:
+; CHECK-NEXT: br label %[[FOR_COND37_PREHEADER_PEEL_NEWPH:.*]]
+; CHECK: [[FOR_COND37_PREHEADER_PEEL_NEWPH]]:
+; CHECK-NEXT: br label %[[FOR_COND37:.*]]
+; CHECK: [[FOR_COND37]]:
+; CHECK-NEXT: [[OFFSET_619:%.*]] = phi i64 [ [[SUB_PTR_DIV:%.*]], %[[FOR_BODY43:.*]] ], [ [[SUB_PTR_DIV_PEEL]], %[[FOR_COND37_PREHEADER_PEEL_NEWPH]] ]
+; CHECK-NEXT: br i1 [[CMP41]], label %[[FOR_BODY43]], label %[[FOR_COND30_LOOPEXIT_LOOPEXIT]]
+; CHECK: [[FOR_BODY43]]:
+; CHECK-NEXT: [[CALL31_I_I:%.*]] = load volatile i64, ptr null, align 8
+; CHECK-NEXT: [[ADD33_I_I:%.*]] = add i64 [[INDVARS_IV]], [[CALL31_I_I]]
+; CHECK-NEXT: [[MUL42_I_I:%.*]] = mul i64 [[TMP1]], [[ADD33_I_I]]
+; CHECK-NEXT: [[ADD43_I_I:%.*]] = add i64 [[MUL42_I_I]], 1
+; CHECK-NEXT: [[MUL52_I_I:%.*]] = mul i64 [[TMP1]], [[ADD43_I_I]]
+; CHECK-NEXT: [[ADD53_I_I:%.*]] = add i64 [[MUL52_I_I]], 1
+; CHECK-NEXT: [[MUL62_I_I:%.*]] = mul i64 [[TMP1]], [[ADD53_I_I]]
+; CHECK-NEXT: [[ADD63_I_I:%.*]] = add i64 [[MUL62_I_I]], 1
+; CHECK-NEXT: [[MUL72_I_I:%.*]] = mul i64 [[INDVARS_IV]], [[ADD63_I_I]]
+; CHECK-NEXT: [[MUL79_I_I:%.*]] = mul i64 [[CALL31_I_I]], [[MUL72_I_I]]
+; CHECK-NEXT: [[DOTIDX1:%.*]] = add i64 [[TMP1]], [[MUL79_I_I]]
+; CHECK-NEXT: [[SUB_PTR_LHS_CAST:%.*]] = shl i64 [[DOTIDX1]], 2
+; CHECK-NEXT: [[SUB_PTR_DIV]] = ashr exact i64 [[SUB_PTR_LHS_CAST]], 1
+; CHECK-NEXT: [[CMP55:%.*]] = icmp sgt i64 [[OFFSET_619]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[CMP55]])
+; CHECK-NEXT: br label %[[FOR_COND37]], !llvm.loop [[LOOP0:![0-9]+]]
+;
+entry:
+ br label %for.cond
+
+for.cond: ; preds = %for.cond2, %entry
+ br label %for.cond2
+
+for.cond2: ; preds = %for.cond.cleanup14, %for.cond
+ %i5.0 = phi i32 [ 0, %for.cond ], [ %inc70, %for.cond.cleanup14 ]
+ %cmp6 = icmp ult i32 %i5.0, %conv5
+ br i1 %cmp6, label %for.cond9, label %for.cond
+
+for.cond9: ; preds = %for.cond16, %for.cond2
+ br i1 %cmp13, label %for.cond16, label %for.cond.cleanup14
+
+for.cond.cleanup14: ; preds = %for.cond9
+ %inc70 = add i32 %i5.0, 1
+ br label %for.cond2
+
+for.cond16: ; preds = %for.cond23, %for.cond9
+ br i1 %cmp20, label %for.cond23, label %for.cond9
+
+for.cond23: ; preds = %for.cond30, %for.cond16
+ br i1 %cmp27, label %for.cond30, label %for.cond16
+
+for.cond30: ; preds = %for.cond37, %for.cond23
+ br i1 %cmp34, label %for.cond37, label %for.cond23
+
+for.cond37: ; preds = %for.body43, %for.cond30
+ %i0.018 = phi i32 [ %inc, %for.body43 ], [ 0, %for.cond30 ]
+ %offset.619 = phi i64 [ %sub.ptr.div, %for.body43 ], [ 0, %for.cond30 ]
+ br i1 %cmp41, label %for.body43, label %for.cond30
+
+for.body43: ; preds = %for.cond37
+ %conv45 = zext i32 %i0.018 to i64
+ %conv50 = zext i32 %i5.0 to i64
+ %call31.i.i = load volatile i64, ptr null, align 8
+ %add33.i.i = add i64 %conv50, %call31.i.i
+ %mul42.i.i = mul i64 %conv45, %add33.i.i
+ %add43.i.i = add i64 %mul42.i.i, 1
+ %mul52.i.i = mul i64 %conv45, %add43.i.i
+ %add53.i.i = add i64 %mul52.i.i, 1
+ %mul62.i.i = mul i64 %conv45, %add53.i.i
+ %add63.i.i = add i64 %mul62.i.i, 1
+ %mul72.i.i = mul i64 %conv50, %add63.i.i
+ %mul79.i.i = mul i64 %call31.i.i, %mul72.i.i
+ %.idx1 = add i64 %conv45, %mul79.i.i
+ %sub.ptr.lhs.cast = shl i64 %.idx1, 2
+ %sub.ptr.div = ashr exact i64 %sub.ptr.lhs.cast, 1
+ %cmp55 = icmp sgt i64 %offset.619, 0
+ call void @llvm.assume(i1 %cmp55)
+ %inc = add i32 %conv5, 1
+ br label %for.cond37
+}
+
+define ptr @_ZNK6Kokkos11DynRankViewIiJNS_10LayoutLeftENS_6SerialEEEclEmmmmmmm(i64 %i0, i64 %i5) local_unnamed_addr {
+; CHECK-LABEL: define ptr @_ZNK6Kokkos11DynRankViewIiJNS_10LayoutLeftENS_6SerialEEEclEmmmmmmm(
+; CHECK-SAME: i64 [[I0:%.*]], i64 [[I5:%.*]]) local_unnamed_addr {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[CALL31_I:%.*]] = load volatile i64, ptr null, align 8
+; CHECK-NEXT: [[ADD33_I:%.*]] = add i64 [[I5]], [[CALL31_I]]
+; CHECK-NEXT: [[MUL42_I:%.*]] = mul i64 [[I0]], [[ADD33_I]]
+; CHECK-NEXT: [[ADD43_I:%.*]] = add i64 [[MUL42_I]], 1
+; CHECK-NEXT: [[MUL52_I:%.*]] = mul i64 [[I0]], [[ADD43_I]]
+; CHECK-NEXT: [[ADD53_I:%.*]] = add i64 [[MUL52_I]], 1
+; CHECK-NEXT: [[MUL62_I:%.*]] = mul i64 [[I0]], [[ADD53_I]]
+; CHECK-NEXT: [[ADD63_I:%.*]] = add i64 [[MUL62_I]], 1
+; CHECK-NEXT: [[MUL72_I:%.*]] = mul i64 [[I5]], [[ADD63_I]]
+; CHECK-NEXT: [[MUL79_I:%.*]] = mul i64 [[CALL31_I]], [[MUL72_I]]
+; CHECK-NEXT: [[ADD80_I:%.*]] = add i64 [[I0]], [[MUL79_I]]
+; CHECK-NEXT: [[ARRAYIDX_I:%.*]] = getelementptr i32, ptr null, i64 [[ADD80_I]]
+; CHECK-NEXT: ret ptr [[ARRAYIDX_I]]
+;
+entry:
+ %call31.i = load volatile i64, ptr null, align 8
+ %add33.i = add i64 %i5, %call31.i
+ %mul42.i = mul i64 %i0, %add33.i
+ %add43.i = add i64 %mul42.i, 1
+ %mul52.i = mul i64 %i0, %add43.i
+ %add53.i = add i64 %mul52.i, 1
+ %mul62.i = mul i64 %i0, %add53.i
+ %add63.i = add i64 %mul62.i, 1
+ %mul72.i = mul i64 %i5, %add63.i
+ %mul79.i = mul i64 %call31.i, %mul72.i
+ %add80.i = add i64 %i0, %mul79.i
+ %arrayidx.i = getelementptr i32, ptr null, i64 %add80.i
+ ret ptr %arrayidx.i
+}
+
+define i64 @_ZNK6Kokkos4ViewIPPPPPPPiJNS_10LayoutLeftENS_6SerialEEE14compute_offsetIJLm0ELm1ELm2ELm3ELm4ELm5ELm6EEJmmmmmmmEEEDaSt16integer_sequenceImJXspT_EEEDpT0_(i64 %index_offsets, i64 %index_offsets9) local_unnamed_addr {
+; CHECK-LABEL: define i64 @_ZNK6Kokkos4ViewIPPPPPPPiJNS_10LayoutLeftENS_6SerialEEE14compute_offsetIJLm0ELm1ELm2ELm3ELm4ELm5ELm6EEJmmmmmmmEEEDaSt16integer_sequenceImJXspT_EEEDpT0_(
+; CHECK-SAME: i64 [[INDEX_OFFSETS:%.*]], i64 [[INDEX_OFFSETS9:%.*]]) local_unnamed_addr {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[CALL31:%.*]] = load volatile i64, ptr null, align 8
+; CHECK-NEXT: [[ADD33:%.*]] = add i64 [[INDEX_OFFSETS9]], [[CALL31]]
+; CHECK-NEXT: [[MUL42:%.*]] = mul i64 [[INDEX_OFFSETS]], [[ADD33]]
+; CHECK-NEXT: [[ADD43:%.*]] = add i64 [[MUL42]], 1
+; CHECK-NEXT: [[MUL52:%.*]] = mul i64 [[INDEX_OFFSETS]], [[ADD43]]
+; CHECK-NEXT: [[ADD53:%.*]] = add i64 [[MUL52]], 1
+; CHECK-NEXT: [[MUL62:%.*]] = mul i64 [[INDEX_OFFSETS]], [[ADD53]]
+; CHECK-NEXT: [[ADD63:%.*]] = add i64 [[MUL62]], 1
+; CHECK-NEXT: [[MUL72:%.*]] = mul i64 [[INDEX_OFFSETS9]], [[ADD63]]
+; CHECK-NEXT: [[MUL79:%.*]] = mul i64 [[CALL31]], [[MUL72]]
+; CHECK-NEXT: [[ADD80:%.*]] = add i64 [[INDEX_OFFSETS]], [[MUL79]]
+; CHECK-NEXT: ret i64 [[ADD80]]
+;
+entry:
+ %call31 = load volatile i64, ptr null, align 8
+ %add33 = add i64 %index_offsets9, %call31
+ %mul42 = mul i64 %index_offsets, %add33
+ %add43 = add i64 %mul42, 1
+ %mul52 = mul i64 %index_offsets, %add43
+ %add53 = add i64 %mul52, 1
+ %mul62 = mul i64 %index_offsets, %add53
+ %add63 = add i64 %mul62, 1
+ %mul72 = mul i64 %index_offsets9, %add63
+ %mul79 = mul i64 %call31, %mul72
+ %add80 = add i64 %index_offsets, %mul79
+ ret i64 %add80
+}
+
+; Function Attrs: nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: write)
+declare void @llvm.assume(i1 noundef) #0
+
+attributes #0 = { nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: write) }
+;.
+; CHECK: [[LOOP0]] = distinct !{[[LOOP0]], [[META1:![0-9]+]]}
+; CHECK: [[META1]] = !{!"llvm.loop.peeled.count", i32 1}
+;.
``````````
</details>
https://github.com/llvm/llvm-project/pull/172234
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