[llvm] 596e4ab - [LCSSA] Forget values we create LCSSA phis for
Florian Hahn via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 29 05:05:49 PDT 2019
Author: Florian Hahn
Date: 2019-10-29T12:05:09Z
New Revision: 596e4ab97a1637d2c7781aed20e3d62bcf07ef5d
URL: https://github.com/llvm/llvm-project/commit/596e4ab97a1637d2c7781aed20e3d62bcf07ef5d
DIFF: https://github.com/llvm/llvm-project/commit/596e4ab97a1637d2c7781aed20e3d62bcf07ef5d.diff
LOG: [LCSSA] Forget values we create LCSSA phis for
Summary:
Currently we only forget the loop we added LCSSA phis for. But SCEV
expressions in other loops could also depend on the instruction we added
a PHI for and currently we do not invalidate those expressions. This can
happen when we use ScalarEvolution before converting a function to LCSSA
form. The SCEV expressions will refer to the non-LCSSA value. If this
SCEV expression is then used with the expander, we do not preserve LCSSA
form.
This patch properly forgets the values we created PHIs for. Those need
to be recomputed again. This patch fixes PR43458.
Currently SCEV::verify does not catch this mismatch and any test would
need to run multiple passes to trigger the error (e.g. -loop-reduce
-loop-unroll). I will also look into catching this kind of mismatch in
the verifier. Also, we currently forget the whole loop in LCSSA and I'll
check if we can be more surgical.
Reviewers: efriedma, sanjoy.google, reames
Reviewed By: efriedma
Subscribers: zzheng, hiraditya, javed.absar, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68194
Added:
llvm/test/Transforms/LoopUnroll/unroll-preserve-scev-lcssa.ll
Modified:
llvm/include/llvm/Transforms/Utils/LoopUtils.h
llvm/lib/Transforms/Utils/LCSSA.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/Transforms/Utils/LoopUtils.h b/llvm/include/llvm/Transforms/Utils/LoopUtils.h
index d32f08717e9b..63cc4484dd5c 100644
--- a/llvm/include/llvm/Transforms/Utils/LoopUtils.h
+++ b/llvm/include/llvm/Transforms/Utils/LoopUtils.h
@@ -73,7 +73,8 @@ bool formDedicatedExitBlocks(Loop *L, DominatorTree *DT, LoopInfo *LI,
///
/// Returns true if any modifications are made.
bool formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
- DominatorTree &DT, LoopInfo &LI);
+ DominatorTree &DT, LoopInfo &LI,
+ ScalarEvolution *SE);
/// Put loop into LCSSA form.
///
diff --git a/llvm/lib/Transforms/Utils/LCSSA.cpp b/llvm/lib/Transforms/Utils/LCSSA.cpp
index 29e7c5260f46..b8a9ae2a498d 100644
--- a/llvm/lib/Transforms/Utils/LCSSA.cpp
+++ b/llvm/lib/Transforms/Utils/LCSSA.cpp
@@ -74,7 +74,8 @@ static bool isExitBlock(BasicBlock *BB,
/// that are outside the current loop. If so, insert LCSSA PHI nodes and
/// rewrite the uses.
bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
- DominatorTree &DT, LoopInfo &LI) {
+ DominatorTree &DT, LoopInfo &LI,
+ ScalarEvolution *SE) {
SmallVector<Use *, 16> UsesToRewrite;
SmallSetVector<PHINode *, 16> PHIsToRemove;
PredIteratorCache PredCache;
@@ -134,6 +135,11 @@ bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
SSAUpdater SSAUpdate(&InsertedPHIs);
SSAUpdate.Initialize(I->getType(), I->getName());
+ // Force re-computation of I, as some users now need to use the new PHI
+ // node.
+ if (SE)
+ SE->forgetValue(I);
+
// Insert the LCSSA phi's into all of the exit blocks dominated by the
// value, and add them to the Phi's map.
for (BasicBlock *ExitBB : ExitBlocks) {
@@ -368,7 +374,7 @@ bool llvm::formLCSSA(Loop &L, DominatorTree &DT, LoopInfo *LI,
Worklist.push_back(&I);
}
}
- Changed = formLCSSAForInstructions(Worklist, DT, *LI);
+ Changed = formLCSSAForInstructions(Worklist, DT, *LI, SE);
// If we modified the code, remove any caches about the loop from SCEV to
// avoid dangling entries.
diff --git a/llvm/test/Transforms/LoopUnroll/unroll-preserve-scev-lcssa.ll b/llvm/test/Transforms/LoopUnroll/unroll-preserve-scev-lcssa.ll
new file mode 100644
index 000000000000..205a51ae3739
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnroll/unroll-preserve-scev-lcssa.ll
@@ -0,0 +1,71 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -loop-reduce -loop-unroll -unroll-runtime -verify-scev -verify-loop-lcssa < %s -S | FileCheck %s
+
+; Test case for PR43458. We check that we do properly invalidate LCSSA phi
+; users in SCEV. Run -loop-reduce first, so SCEV is already populated.
+
+define void @spam() {
+; CHECK-LABEL: @spam(
+; CHECK-NEXT: bb:
+; CHECK-NEXT: br label [[BB3:%.*]]
+; CHECK: bb3:
+; CHECK-NEXT: br i1 false, label [[BB9:%.*]], label [[BB5_PREHEADER:%.*]]
+; CHECK: bb5.preheader:
+; CHECK-NEXT: br label [[BB5:%.*]]
+; CHECK: bb5:
+; CHECK-NEXT: br label [[BB9]]
+; CHECK: bb9:
+; CHECK-NEXT: [[TMP10:%.*]] = phi i64 [ 0, [[BB3]] ], [ 5, [[BB5]] ]
+; CHECK-NEXT: [[TMP11:%.*]] = trunc i64 [[TMP10]] to i32
+; CHECK-NEXT: [[TMP21:%.*]] = sext i32 [[TMP11]] to i64
+; CHECK-NEXT: [[TMP22:%.*]] = icmp slt i64 0, [[TMP21]]
+; CHECK-NEXT: br i1 [[TMP22]], label [[BB24_PREHEADER:%.*]], label [[BB29:%.*]]
+; CHECK: bb24.preheader:
+; CHECK-NEXT: br label [[BB24:%.*]]
+; CHECK: bb24:
+; CHECK-NEXT: [[TMP25:%.*]] = phi i64 [ [[TMP26:%.*]], [[BB24]] ], [ 0, [[BB24_PREHEADER]] ]
+; CHECK-NEXT: [[TMP26]] = add nuw nsw i64 [[TMP25]], 1
+; CHECK-NEXT: [[TMP27:%.*]] = icmp slt i64 [[TMP26]], [[TMP21]]
+; CHECK-NEXT: br i1 [[TMP27]], label [[BB24]], label [[BB29_LOOPEXIT:%.*]]
+; CHECK: bb29.loopexit:
+; CHECK-NEXT: br label [[BB29]]
+; CHECK: bb29:
+; CHECK-NEXT: ret void
+;
+bb:
+ br label %bb3
+
+bb3: ; preds = %bb9, %bb
+ %pv1 = phi i64 [ 0, %bb ], [ %iv1, %bb9]
+ %c1 = icmp eq i64 %pv1, 5
+ br i1 %c1, label %bb9, label %bb5
+
+bb5: ; preds = %bb5, %bb3
+ %pv = phi i64 [ 0, %bb3], [ %tmp6, %bb5]
+ %tmp6 = add nsw i64 %pv, 1
+ %cond = icmp eq i64 %tmp6, 5
+ br i1 %cond, label %bb8, label %bb5
+
+bb8: ; preds = %bb5
+ br label %bb9
+
+bb9: ; preds = %bb8, %bb3
+ %tmp10 = phi i64 [ 0, %bb3 ], [ %tmp6, %bb8 ]
+ %tmp11 = trunc i64 %tmp10 to i32
+ %iv1 = add nsw i64 %pv1, 1
+ br i1 false, label %bb3, label %bb20
+
+bb20: ; preds = %bb9
+ %tmp21 = sext i32 %tmp11 to i64
+ %tmp22 = icmp slt i64 0, %tmp21
+ br i1 %tmp22, label %bb24, label %bb29
+
+bb24: ; preds = %bb24, %bb20
+ %tmp25 = phi i64 [ %tmp26, %bb24 ], [ 0, %bb20 ]
+ %tmp26 = add nuw nsw i64 %tmp25, 1
+ %tmp27 = icmp slt i64 %tmp26, %tmp21
+ br i1 %tmp27, label %bb24, label %bb29
+
+bb29: ; preds = %bb24, %bb20
+ ret void
+}
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