[llvm] [SCEV][LV] Invalidate LCSSA exit phis more thoroughly (PR #69909)
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Thu Nov 16 01:15:10 PST 2023
https://github.com/nikic updated https://github.com/llvm/llvm-project/pull/69909
>From 7711c01680ad1c82e7dfa0a4e4975bd68f86b021 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Mon, 23 Oct 2023 11:55:02 +0200
Subject: [PATCH] [SCEV][LV] Invalidate LCSSA exit phis more thoroughly
Fix this an alternative to #69886. The basic problem is that
SCEV can look through trivial LCSSA phis. When the phi node
later becomes non-trivial, we do invalidate it, but this doesn't
catch uses that are not covered by the IR use-def walk, such as
thoe in BECounts.
Fix this by adding a special invalidation method for LCSSA phis,
which will also invalidate all the SCEVUnknowns used by the LCSSA
phi node.
We should probably also use this invalidation method in other
places that add predecessors to exit blocks, such as loop unroling
and loop peeling.
---
llvm/include/llvm/Analysis/ScalarEvolution.h | 4 +
llvm/lib/Analysis/ScalarEvolution.cpp | 38 ++++++++
.../Transforms/Vectorize/LoopVectorize.cpp | 2 +-
llvm/test/Transforms/LoopVectorize/pr66616.ll | 95 +++++++++++++++++++
4 files changed, 138 insertions(+), 1 deletion(-)
create mode 100644 llvm/test/Transforms/LoopVectorize/pr66616.ll
diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index 234c05f48d8edfa..4f1237c4b1f92b7 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -943,6 +943,10 @@ class ScalarEvolution {
/// def-use chain linking it to a loop.
void forgetValue(Value *V);
+ /// Forget LCSSA phi node V of loop L to which a new predecessor was added,
+ /// such that it may no longer be trivial.
+ void forgetLcssaPhiWithNewPredecessor(Loop *L, PHINode *V);
+
/// Called when the client has changed the disposition of values in
/// this loop.
///
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 8b3fc8d126050cc..9670e5309b32f5a 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -8410,6 +8410,44 @@ void ScalarEvolution::forgetValue(Value *V) {
forgetMemoizedResults(ToForget);
}
+void ScalarEvolution::forgetLcssaPhiWithNewPredecessor(Loop *L, PHINode *V) {
+ if (!isSCEVable(V->getType()))
+ return;
+
+ // If SCEV looked through a trivial LCSSA phi node, we might have SCEV's
+ // directly using a SCEVUnknown/SCEVAddRec defined in the loop. After an
+ // extra predecessor is added, this is no longer valid. Find all Unknowns and
+ // AddRecs defined in the loop and invalidate any SCEV's making use of them.
+ if (const SCEV *S = getExistingSCEV(V)) {
+ struct InvalidationRootCollector {
+ Loop *L;
+ SmallVector<const SCEV *, 8> Roots;
+
+ InvalidationRootCollector(Loop *L) : L(L) {}
+
+ bool follow(const SCEV *S) {
+ if (auto *SU = dyn_cast<SCEVUnknown>(S)) {
+ if (auto *I = dyn_cast<Instruction>(SU->getValue()))
+ if (L->contains(I))
+ Roots.push_back(S);
+ } else if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(S)) {
+ if (L->contains(AddRec->getLoop()))
+ Roots.push_back(S);
+ }
+ return true;
+ }
+ bool isDone() const { return false; }
+ };
+
+ InvalidationRootCollector C(L);
+ visitAll(S, C);
+ forgetMemoizedResults(C.Roots);
+ }
+
+ // Also perform the normal invalidation.
+ forgetValue(V);
+}
+
void ScalarEvolution::forgetLoopDispositions() { LoopDispositions.clear(); }
void ScalarEvolution::forgetBlockAndLoopDispositions(Value *V) {
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index e9d0315d114f65c..ad59f6f1a7f74ff 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -3566,7 +3566,7 @@ void InnerLoopVectorizer::fixVectorizedLoop(VPTransformState &State,
OrigLoop->getExitBlocks(ExitBlocks);
for (BasicBlock *Exit : ExitBlocks)
for (PHINode &PN : Exit->phis())
- PSE.getSE()->forgetValue(&PN);
+ PSE.getSE()->forgetLcssaPhiWithNewPredecessor(OrigLoop, &PN);
VPBasicBlock *LatchVPBB = Plan.getVectorLoopRegion()->getExitingBasicBlock();
Loop *VectorLoop = LI->getLoopFor(State.CFG.VPBB2IRBB[LatchVPBB]);
diff --git a/llvm/test/Transforms/LoopVectorize/pr66616.ll b/llvm/test/Transforms/LoopVectorize/pr66616.ll
new file mode 100644
index 000000000000000..2fb7f88e5341e5f
--- /dev/null
+++ b/llvm/test/Transforms/LoopVectorize/pr66616.ll
@@ -0,0 +1,95 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
+; RUN: opt -passes="print<scalar-evolution>,loop-vectorize" --verify-scev -S < %s -force-vector-width=4 2>/dev/null | FileCheck %s
+
+; Make sure users of SCEVUnknowns from the scalar loop are invalidated.
+
+define void @pr66616(ptr %ptr) {
+; CHECK-LABEL: define void @pr66616(
+; CHECK-SAME: ptr [[PTR:%.*]]) {
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br i1 false, label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK: vector.ph:
+; CHECK-NEXT: br label [[VECTOR_BODY:%.*]]
+; CHECK: vector.body:
+; CHECK-NEXT: [[INDEX:%.*]] = phi i32 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[PTR]], align 4
+; CHECK-NEXT: [[BROADCAST_SPLATINSERT:%.*]] = insertelement <4 x i32> poison, i32 [[TMP0]], i64 0
+; CHECK-NEXT: [[BROADCAST_SPLAT:%.*]] = shufflevector <4 x i32> [[BROADCAST_SPLATINSERT]], <4 x i32> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT: [[TMP1:%.*]] = add <4 x i32> [[BROADCAST_SPLAT]], <i32 1, i32 1, i32 1, i32 1>
+; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 4
+; CHECK-NEXT: [[TMP2:%.*]] = icmp eq i32 [[INDEX_NEXT]], 256
+; CHECK-NEXT: br i1 [[TMP2]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK: middle.block:
+; CHECK-NEXT: [[TMP3:%.*]] = extractelement <4 x i32> [[TMP1]], i32 3
+; CHECK-NEXT: br i1 true, label [[PREHEADER:%.*]], label [[SCALAR_PH]]
+; CHECK: scalar.ph:
+; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i8 [ 0, [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT: br label [[LOOP_1:%.*]]
+; CHECK: loop.1:
+; CHECK-NEXT: [[IV_1:%.*]] = phi i8 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[INC:%.*]], [[LOOP_1]] ]
+; CHECK-NEXT: [[LOAD:%.*]] = load i32, ptr [[PTR]], align 4
+; CHECK-NEXT: [[ADD3:%.*]] = add i32 [[LOAD]], 1
+; CHECK-NEXT: [[INC]] = add i8 [[IV_1]], 1
+; CHECK-NEXT: [[COND1:%.*]] = icmp eq i8 [[INC]], 0
+; CHECK-NEXT: br i1 [[COND1]], label [[PREHEADER]], label [[LOOP_1]], !llvm.loop [[LOOP3:![0-9]+]]
+; CHECK: preheader:
+; CHECK-NEXT: [[ADD3_LCSSA:%.*]] = phi i32 [ [[ADD3]], [[LOOP_1]] ], [ [[TMP3]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT: [[TMP4:%.*]] = sub i32 0, [[ADD3_LCSSA]]
+; CHECK-NEXT: [[TMP5:%.*]] = zext i32 [[TMP4]] to i64
+; CHECK-NEXT: [[TMP6:%.*]] = add nuw nsw i64 [[TMP5]], 1
+; CHECK-NEXT: [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[TMP6]], 4
+; CHECK-NEXT: br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH2:%.*]], label [[VECTOR_PH3:%.*]]
+; CHECK: vector.ph3:
+; CHECK-NEXT: [[N_MOD_VF:%.*]] = urem i64 [[TMP6]], 4
+; CHECK-NEXT: [[N_VEC:%.*]] = sub i64 [[TMP6]], [[N_MOD_VF]]
+; CHECK-NEXT: [[DOTCAST:%.*]] = trunc i64 [[N_VEC]] to i32
+; CHECK-NEXT: [[IND_END:%.*]] = add i32 [[ADD3_LCSSA]], [[DOTCAST]]
+; CHECK-NEXT: [[IND_END5:%.*]] = getelementptr i8, ptr [[PTR]], i64 [[N_VEC]]
+; CHECK-NEXT: br label [[VECTOR_BODY7:%.*]]
+; CHECK: vector.body7:
+; CHECK-NEXT: [[INDEX8:%.*]] = phi i64 [ 0, [[VECTOR_PH3]] ], [ [[INDEX_NEXT9:%.*]], [[VECTOR_BODY7]] ]
+; CHECK-NEXT: [[INDEX_NEXT9]] = add nuw i64 [[INDEX8]], 4
+; CHECK-NEXT: [[TMP7:%.*]] = icmp eq i64 [[INDEX_NEXT9]], [[N_VEC]]
+; CHECK-NEXT: br i1 [[TMP7]], label [[MIDDLE_BLOCK1:%.*]], label [[VECTOR_BODY7]], !llvm.loop [[LOOP4:![0-9]+]]
+; CHECK: middle.block1:
+; CHECK-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[TMP6]], [[N_VEC]]
+; CHECK-NEXT: br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH2]]
+; CHECK: scalar.ph2:
+; CHECK-NEXT: [[BC_RESUME_VAL4:%.*]] = phi i32 [ [[IND_END]], [[MIDDLE_BLOCK1]] ], [ [[ADD3_LCSSA]], [[PREHEADER]] ]
+; CHECK-NEXT: [[BC_RESUME_VAL6:%.*]] = phi ptr [ [[IND_END5]], [[MIDDLE_BLOCK1]] ], [ [[PTR]], [[PREHEADER]] ]
+; CHECK-NEXT: br label [[LOOP_2:%.*]]
+; CHECK: loop.2:
+; CHECK-NEXT: [[IV_2:%.*]] = phi i32 [ [[IV_2_I:%.*]], [[LOOP_2]] ], [ [[BC_RESUME_VAL4]], [[SCALAR_PH2]] ]
+; CHECK-NEXT: [[IV_3:%.*]] = phi ptr [ [[IV_3_I:%.*]], [[LOOP_2]] ], [ [[BC_RESUME_VAL6]], [[SCALAR_PH2]] ]
+; CHECK-NEXT: [[IV_2_I]] = add i32 [[IV_2]], 1
+; CHECK-NEXT: [[IV_3_I]] = getelementptr i8, ptr [[IV_3]], i64 1
+; CHECK-NEXT: [[COND2:%.*]] = icmp eq i32 [[IV_2]], 0
+; CHECK-NEXT: br i1 [[COND2]], label [[EXIT]], label [[LOOP_2]], !llvm.loop [[LOOP5:![0-9]+]]
+; CHECK: exit:
+; CHECK-NEXT: ret void
+;
+entry:
+ br label %loop.1
+
+loop.1:
+ %iv.1 = phi i8 [ 0, %entry ], [ %inc, %loop.1 ]
+ %load = load i32, ptr %ptr, align 4
+ %add3 = add i32 %load, 1
+ %inc = add i8 %iv.1, 1
+ %cond1 = icmp eq i8 %inc, 0
+ br i1 %cond1, label %preheader, label %loop.1
+
+preheader:
+ br label %loop.2
+
+loop.2:
+ %iv.2 = phi i32 [ %iv.2.i, %loop.2 ], [ %add3, %preheader ]
+ %iv.3 = phi ptr [ %iv.3.i, %loop.2 ], [ %ptr, %preheader ]
+ %iv.2.i = add i32 %iv.2, 1
+ %iv.3.i = getelementptr i8, ptr %iv.3, i64 1
+ %cond2 = icmp eq i32 %iv.2, 0
+ br i1 %cond2, label %exit, label %loop.2
+
+exit:
+ ret void
+}
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