[llvm-branch-commits] [llvm] de6d43f - Revert "[LoopNest] Allow empty basic blocks without loops"
Whitney Tsang via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Mon Jan 4 12:46:40 PST 2021
Author: Whitney Tsang
Date: 2021-01-04T20:42:21Z
New Revision: de6d43f16cbaf2eae6fa161ea6e811b8f5f45174
URL: https://github.com/llvm/llvm-project/commit/de6d43f16cbaf2eae6fa161ea6e811b8f5f45174
DIFF: https://github.com/llvm/llvm-project/commit/de6d43f16cbaf2eae6fa161ea6e811b8f5f45174.diff
LOG: Revert "[LoopNest] Allow empty basic blocks without loops"
This reverts commit 9a17bff4f715a9f3ec89f4eacae8fdea1b74fe79.
Added:
Modified:
llvm/include/llvm/Analysis/LoopNestAnalysis.h
llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
llvm/lib/Analysis/LoopNestAnalysis.cpp
llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll
Removed:
################################################################################
diff --git a/llvm/include/llvm/Analysis/LoopNestAnalysis.h b/llvm/include/llvm/Analysis/LoopNestAnalysis.h
index 692909db8341..4d77d735819f 100644
--- a/llvm/include/llvm/Analysis/LoopNestAnalysis.h
+++ b/llvm/include/llvm/Analysis/LoopNestAnalysis.h
@@ -128,12 +128,6 @@ class LoopNest {
[](const Loop *L) { return L->isLoopSimplifyForm(); });
}
- /// Return true if all loops in the loop nest are in rotated form.
- bool areAllLoopsRotatedForm() const {
- return std::all_of(Loops.begin(), Loops.end(),
- [](const Loop *L) { return L->isRotatedForm(); });
- }
-
StringRef getName() const { return Loops.front()->getName(); }
protected:
diff --git a/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h b/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
index fd5a7daf3add..64c569de1f58 100644
--- a/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ b/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -244,12 +244,6 @@ unsigned SplitAllCriticalEdges(Function &F,
const CriticalEdgeSplittingOptions &Options =
CriticalEdgeSplittingOptions());
-/// Recursivelly traverse all empty 'single successor' basic blocks of \p From
-/// (if there are any). Return the last basic block found or \p End if it was
-/// reached during the search.
-const BasicBlock &skipEmptyBlockUntil(const BasicBlock *From,
- const BasicBlock *End);
-
/// Split the edge connecting the specified blocks, and return the newly created
/// basic block between \p From and \p To.
BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To,
diff --git a/llvm/lib/Analysis/LoopNestAnalysis.cpp b/llvm/lib/Analysis/LoopNestAnalysis.cpp
index abc219a8bd32..ef10b7e97461 100644
--- a/llvm/lib/Analysis/LoopNestAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopNestAnalysis.cpp
@@ -16,7 +16,6 @@
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/PostDominators.h"
#include "llvm/Analysis/ValueTracking.h"
-#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
@@ -254,66 +253,49 @@ static bool checkLoopsStructure(const Loop &OuterLoop, const Loop &InnerLoop,
// Ensure the only branch that may exist between the loops is the inner loop
// guard.
if (OuterLoopHeader != InnerLoopPreHeader) {
- const BasicBlock &SingleSucc =
- skipEmptyBlockUntil(OuterLoopHeader, InnerLoopPreHeader);
-
- // no conditional branch present
- if (&SingleSucc != InnerLoopPreHeader) {
- const BranchInst *BI = dyn_cast<BranchInst>(SingleSucc.getTerminator());
-
- if (!BI || BI != InnerLoop.getLoopGuardBranch())
- return false;
-
- bool InnerLoopExitContainsLCSSA = ContainsLCSSAPhi(*InnerLoopExit);
-
- // The successors of the inner loop guard should be the inner loop
- // preheader or the outer loop latch possibly through empty blocks.
- for (const BasicBlock *Succ : BI->successors()) {
- const BasicBlock *PotentialInnerPreHeader = Succ;
- const BasicBlock *PotentialOuterLatch = Succ;
-
- // Ensure the inner loop guard successor is empty before skipping
- // blocks.
- if (Succ->getInstList().size() == 1) {
- PotentialInnerPreHeader =
- &skipEmptyBlockUntil(Succ, InnerLoopPreHeader);
- PotentialOuterLatch = &skipEmptyBlockUntil(Succ, OuterLoopLatch);
- }
-
- if (PotentialInnerPreHeader == InnerLoopPreHeader)
- continue;
- if (PotentialOuterLatch == OuterLoopLatch)
- continue;
-
- // If `InnerLoopExit` contains LCSSA Phi instructions, additional block
- // may be inserted before the `OuterLoopLatch` to which `BI` jumps. The
- // loops are still considered perfectly nested if the extra block only
- // contains Phi instructions from InnerLoopExit and OuterLoopHeader.
- if (InnerLoopExitContainsLCSSA && IsExtraPhiBlock(*Succ) &&
- Succ->getSingleSuccessor() == OuterLoopLatch) {
- // Points to the extra block so that we can reference it later in the
- // final check. We can also conclude that the inner loop is
- // guarded and there exists LCSSA Phi node in the exit block later if
- // we see a non-null `ExtraPhiBlock`.
- ExtraPhiBlock = Succ;
- continue;
- }
-
- DEBUG_WITH_TYPE(VerboseDebug, {
- dbgs() << "Inner loop guard successor " << Succ->getName()
- << " doesn't lead to inner loop preheader or "
- "outer loop latch.\n";
- });
- return false;
+ const BranchInst *BI =
+ dyn_cast<BranchInst>(OuterLoopHeader->getTerminator());
+
+ if (!BI || BI != InnerLoop.getLoopGuardBranch())
+ return false;
+
+ bool InnerLoopExitContainsLCSSA = ContainsLCSSAPhi(*InnerLoopExit);
+
+ // The successors of the inner loop guard should be the inner loop
+ // preheader and the outer loop latch.
+ for (const BasicBlock *Succ : BI->successors()) {
+ if (Succ == InnerLoopPreHeader)
+ continue;
+ if (Succ == OuterLoopLatch)
+ continue;
+
+ // If `InnerLoopExit` contains LCSSA Phi instructions, additional block
+ // may be inserted before the `OuterLoopLatch` to which `BI` jumps. The
+ // loops are still considered perfectly nested if the extra block only
+ // contains Phi instructions from InnerLoopExit and OuterLoopHeader.
+ if (InnerLoopExitContainsLCSSA && IsExtraPhiBlock(*Succ) &&
+ Succ->getSingleSuccessor() == OuterLoopLatch) {
+ // Points to the extra block so that we can reference it later in the
+ // final check. We can also conclude that the inner loop is
+ // guarded and there exists LCSSA Phi node in the exit block later if we
+ // see a non-null `ExtraPhiBlock`.
+ ExtraPhiBlock = Succ;
+ continue;
}
+
+ DEBUG_WITH_TYPE(VerboseDebug, {
+ dbgs() << "Inner loop guard successor " << Succ->getName()
+ << " doesn't lead to inner loop preheader or "
+ "outer loop latch.\n";
+ });
+ return false;
}
}
- // Ensure the inner loop exit block lead to the outer loop latch possibly
- // through empty blocks.
- const BasicBlock &SuccInner =
- skipEmptyBlockUntil(InnerLoop.getExitBlock(), OuterLoopLatch);
- if (&SuccInner != OuterLoopLatch && &SuccInner != ExtraPhiBlock) {
+ // Ensure the inner loop exit block leads to the outer loop latch.
+ const BasicBlock *SuccInner = InnerLoopExit->getSingleSuccessor();
+ if (!SuccInner ||
+ (SuccInner != OuterLoopLatch && SuccInner != ExtraPhiBlock)) {
DEBUG_WITH_TYPE(
VerboseDebug,
dbgs() << "Inner loop exit block " << *InnerLoopExit
diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 1b89ebe2f7db..5b8bc184daca 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -494,31 +494,6 @@ void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
}
-const BasicBlock &llvm::skipEmptyBlockUntil(const BasicBlock *From,
- const BasicBlock *End) {
- assert(From && "Expecting valid From");
- assert(End && "Expecting valid End");
-
- if (From == End || !From->getSingleSuccessor())
- return *From;
-
- auto IsEmpty = [](const BasicBlock *BB) {
- return (BB->getInstList().size() == 1);
- };
-
- // Visited is used to avoid running into an infinite loop.
- SmallPtrSet<const BasicBlock *, 4> Visited;
- const BasicBlock *BB = From->getSingleSuccessor();
- const BasicBlock *PredBB = BB;
- while (BB && BB != End && IsEmpty(BB) && !Visited.count(BB)) {
- Visited.insert(BB);
- PredBB = BB;
- BB = BB->getSingleSuccessor();
- }
-
- return (BB == End) ? *End : *PredBB;
-}
-
BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, DominatorTree *DT,
LoopInfo *LI, MemorySSAUpdater *MSSAU) {
unsigned SuccNum = GetSuccessorNumber(BB, Succ);
diff --git a/llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll b/llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll
index 7593d6f1748b..b7b3b7a7c93e 100644
--- a/llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll
+++ b/llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll
@@ -85,55 +85,6 @@ perf_nest_2D_2_loop_i_end:
ret void
}
-define void @perf_nest_2D_3(i32** %y, i32** %x, i64 signext %nx, i64 signext %ny) {
-; CHECK-LABEL: IsPerfect=true, Depth=1, OutermostLoop: perf_nest_2D_3_loop_j, Loops: ( perf_nest_2D_3_loop_j )
-; CHECK-LABEL: IsPerfect=true, Depth=2, OutermostLoop: perf_nest_2D_3_loop_i, Loops: ( perf_nest_2D_3_loop_i perf_nest_2D_3_loop_j )
-entry:
- br label %perf_nest_2D_3_loop_i
-
-perf_nest_2D_3_loop_i:
- %i = phi i64 [ 0, %entry ], [ %inc13, %inc_i ]
- %cmp21 = icmp slt i64 0, %ny
- br label %singleSucc
-
-singleSucc:
- br i1 %cmp21, label %preheader.j, label %for.end
-
-preheader.j:
- br label %perf_nest_2D_3_loop_j
-
-perf_nest_2D_3_loop_j:
- %j = phi i64 [ 0, %preheader.j ], [ %inc, %inc_j ]
- %arrayidx = getelementptr inbounds i32*, i32** %x, i64 %j
- %0 = load i32*, i32** %arrayidx, align 8
- %arrayidx6 = getelementptr inbounds i32, i32* %0, i64 %j
- %1 = load i32, i32* %arrayidx6, align 4
- %arrayidx8 = getelementptr inbounds i32*, i32** %y, i64 %j
- %2 = load i32*, i32** %arrayidx8, align 8
- %arrayidx11 = getelementptr inbounds i32, i32* %2, i64 %i
- store i32 %1, i32* %arrayidx11, align 4
- br label %inc_j
-
-inc_j:
- %inc = add nsw i64 %j, 1
- %cmp2 = icmp slt i64 %inc, %ny
- br i1 %cmp2, label %perf_nest_2D_3_loop_j, label %for.exit
-
-for.exit:
- br label %for.end
-
-for.end:
- br label %inc_i
-
-inc_i:
- %inc13 = add nsw i64 %i, 1
- %cmp = icmp slt i64 %inc13, %nx
- br i1 %cmp, label %perf_nest_2D_3_loop_i, label %perf_nest_2D_3_loop_i_end
-
-perf_nest_2D_3_loop_i_end:
- ret void
-}
-
; Test a perfect 3-dim loop nest of the form:
; for (i=0; i<nx; ++i)
; for (j=0; j<ny; ++j)
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