[llvm] r224740 - [LCSSA] Handle PHI insertion in disjoint loops
Bruno Cardoso Lopes
bruno.cardoso at gmail.com
Mon Dec 22 14:35:46 PST 2014
Author: bruno
Date: Mon Dec 22 16:35:46 2014
New Revision: 224740
URL: http://llvm.org/viewvc/llvm-project?rev=224740&view=rev
Log:
[LCSSA] Handle PHI insertion in disjoint loops
Take two disjoint Loops L1 and L2.
LoopSimplify fails to simplify some loops (e.g. when indirect branches
are involved). In such situations, it can happen that an exit for L1 is
the header of L2. Thus, when we create PHIs in one of such exits we are
also inserting PHIs in L2 header.
This could break LCSSA form for L2 because these inserted PHIs can also
have uses in L2 exits, which are never handled in the current
implementation. Provide a fix for this corner case and test that we
don't assert/crash on that.
Differential Revision: http://reviews.llvm.org/D6624
rdar://problem/19166231
Modified:
llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h
llvm/trunk/lib/Transforms/Scalar/LICM.cpp
llvm/trunk/lib/Transforms/Utils/LCSSA.cpp
llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp
llvm/trunk/test/Transforms/LCSSA/indirectbr.ll
Modified: llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h?rev=224740&r1=224739&r2=224740&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h (original)
+++ llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h Mon Dec 22 16:35:46 2014
@@ -49,7 +49,8 @@ bool simplifyLoop(Loop *L, DominatorTree
/// If ScalarEvolution is passed in, it will be preserved.
///
/// Returns true if any modifications are made to the loop.
-bool formLCSSA(Loop &L, DominatorTree &DT, ScalarEvolution *SE = nullptr);
+bool formLCSSA(Loop &L, DominatorTree &DT, LoopInfo *LI,
+ ScalarEvolution *SE = nullptr);
/// \brief Put a loop nest into LCSSA form.
///
@@ -60,7 +61,7 @@ bool formLCSSA(Loop &L, DominatorTree &D
/// If ScalarEvolution is passed in, it will be preserved.
///
/// Returns true if any modifications are made to the loop.
-bool formLCSSARecursively(Loop &L, DominatorTree &DT,
+bool formLCSSARecursively(Loop &L, DominatorTree &DT, LoopInfo *LI,
ScalarEvolution *SE = nullptr);
}
Modified: llvm/trunk/lib/Transforms/Scalar/LICM.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LICM.cpp?rev=224740&r1=224739&r2=224740&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LICM.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LICM.cpp Mon Dec 22 16:35:46 2014
@@ -316,7 +316,8 @@ bool LICM::runOnLoop(Loop *L, LPPassMana
// SSAUpdater strategy during promotion that was LCSSA aware and reformed
// it as it went.
if (Changed)
- formLCSSARecursively(*L, *DT, getAnalysisIfAvailable<ScalarEvolution>());
+ formLCSSARecursively(*L, *DT, LI,
+ getAnalysisIfAvailable<ScalarEvolution>());
}
// Check that neither this loop nor its parent have had LCSSA broken. LICM is
Modified: llvm/trunk/lib/Transforms/Utils/LCSSA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LCSSA.cpp?rev=224740&r1=224739&r2=224740&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/LCSSA.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/LCSSA.cpp Mon Dec 22 16:35:46 2014
@@ -61,7 +61,7 @@ static bool isExitBlock(BasicBlock *BB,
/// uses.
static bool processInstruction(Loop &L, Instruction &Inst, DominatorTree &DT,
const SmallVectorImpl<BasicBlock *> &ExitBlocks,
- PredIteratorCache &PredCache) {
+ PredIteratorCache &PredCache, LoopInfo *LI) {
SmallVector<Use *, 16> UsesToRewrite;
BasicBlock *InstBB = Inst.getParent();
@@ -94,6 +94,7 @@ static bool processInstruction(Loop &L,
DomTreeNode *DomNode = DT.getNode(DomBB);
SmallVector<PHINode *, 16> AddedPHIs;
+ SmallVector<PHINode *, 8> PostProcessPHIs;
SSAUpdater SSAUpdate;
SSAUpdate.Initialize(Inst.getType(), Inst.getName());
@@ -131,6 +132,18 @@ static bool processInstruction(Loop &L,
// Remember that this phi makes the value alive in this block.
SSAUpdate.AddAvailableValue(ExitBB, PN);
+
+ // LoopSimplify might fail to simplify some loops (e.g. when indirect
+ // branches are involved). In such situations, it might happen that an exit
+ // for Loop L1 is the header of a disjoint Loop L2. Thus, when we create
+ // PHIs in such an exit block, we are also inserting PHIs into L2's header.
+ // This could break LCSSA form for L2 because these inserted PHIs can also
+ // have uses outside of L2. Remember all PHIs in such situation as to
+ // revisit than later on. FIXME: Remove this if indirectbr support into
+ // LoopSimplify gets improved.
+ if (auto *OtherLoop = LI->getLoopFor(ExitBB))
+ if (!L.contains(OtherLoop))
+ PostProcessPHIs.push_back(PN);
}
// Rewrite all uses outside the loop in terms of the new PHIs we just
@@ -157,6 +170,25 @@ static bool processInstruction(Loop &L,
SSAUpdate.RewriteUse(*UsesToRewrite[i]);
}
+ // Post process PHI instructions that were inserted into another disjoint loop
+ // and update their exits properly.
+ for (auto *I : PostProcessPHIs) {
+ if (I->use_empty())
+ continue;
+
+ BasicBlock *PHIBB = I->getParent();
+ Loop *OtherLoop = LI->getLoopFor(PHIBB);
+ SmallVector<BasicBlock *, 8> EBs;
+ OtherLoop->getExitBlocks(EBs);
+ if (EBs.empty())
+ continue;
+
+ // Recurse and re-process each PHI instruction. FIXME: we should really
+ // convert this entire thing to a worklist approach where we process a
+ // vector of instructions...
+ processInstruction(*OtherLoop, *I, DT, EBs, PredCache, LI);
+ }
+
// Remove PHI nodes that did not have any uses rewritten.
for (unsigned i = 0, e = AddedPHIs.size(); i != e; ++i) {
if (AddedPHIs[i]->use_empty())
@@ -180,7 +212,8 @@ blockDominatesAnExit(BasicBlock *BB,
return false;
}
-bool llvm::formLCSSA(Loop &L, DominatorTree &DT, ScalarEvolution *SE) {
+bool llvm::formLCSSA(Loop &L, DominatorTree &DT, LoopInfo *LI,
+ ScalarEvolution *SE) {
bool Changed = false;
// Get the set of exiting blocks.
@@ -212,7 +245,7 @@ bool llvm::formLCSSA(Loop &L, DominatorT
!isa<PHINode>(I->user_back())))
continue;
- Changed |= processInstruction(L, *I, DT, ExitBlocks, PredCache);
+ Changed |= processInstruction(L, *I, DT, ExitBlocks, PredCache, LI);
}
}
@@ -228,15 +261,15 @@ bool llvm::formLCSSA(Loop &L, DominatorT
}
/// Process a loop nest depth first.
-bool llvm::formLCSSARecursively(Loop &L, DominatorTree &DT,
+bool llvm::formLCSSARecursively(Loop &L, DominatorTree &DT, LoopInfo *LI,
ScalarEvolution *SE) {
bool Changed = false;
// Recurse depth-first through inner loops.
- for (Loop::iterator LI = L.begin(), LE = L.end(); LI != LE; ++LI)
- Changed |= formLCSSARecursively(**LI, DT, SE);
+ for (Loop::iterator I = L.begin(), E = L.end(); I != E; ++I)
+ Changed |= formLCSSARecursively(**I, DT, LI, SE);
- Changed |= formLCSSA(L, DT, SE);
+ Changed |= formLCSSA(L, DT, LI, SE);
return Changed;
}
@@ -291,7 +324,7 @@ bool LCSSA::runOnFunction(Function &F) {
// Simplify each loop nest in the function.
for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
- Changed |= formLCSSARecursively(**I, *DT, SE);
+ Changed |= formLCSSARecursively(**I, *DT, LI, SE);
return Changed;
}
Modified: llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp?rev=224740&r1=224739&r2=224740&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp Mon Dec 22 16:35:46 2014
@@ -544,7 +544,7 @@ bool llvm::UnrollLoop(Loop *L, unsigned
while (OuterL->getParentLoop() != LatchLoop)
OuterL = OuterL->getParentLoop();
- formLCSSARecursively(*OuterL, *DT, SE);
+ formLCSSARecursively(*OuterL, *DT, LI, SE);
}
}
Modified: llvm/trunk/test/Transforms/LCSSA/indirectbr.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LCSSA/indirectbr.ll?rev=224740&r1=224739&r2=224740&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LCSSA/indirectbr.ll (original)
+++ llvm/trunk/test/Transforms/LCSSA/indirectbr.ll Mon Dec 22 16:35:46 2014
@@ -1,11 +1,11 @@
-; RUN: opt < %s -lcssa -verify-loop-info -verify-dom-info -disable-output
-; PR5437
+; RUN: opt < %s -loop-simplify -lcssa -verify-loop-info -verify-dom-info -S | FileCheck %s
; LCSSA should work correctly in the case of an indirectbr that exits
; the loop, and the loop has exits with predecessors not within the loop
; (and btw these edges are unsplittable due to the indirectbr).
-
-define i32 @js_Interpret() nounwind {
+; PR5437
+define i32 @test0() nounwind {
+; CHECK-LABEL: @test0
entry:
br i1 undef, label %"4", label %"3"
@@ -540,3 +540,35 @@ entry:
"1862": ; preds = %"1836", %"692"
unreachable
}
+
+; An exit for Loop L1 may be the header of a disjoint Loop L2. Thus, when we
+; create PHIs in one of such exits we are also inserting PHIs in L2 header. This
+; could break LCSSA form for L2 because these inserted PHIs can also have uses
+; in L2 exits. Test that we don't assert/crash on that.
+define void @test1() {
+; CHECK-LABEL: @test1
+ br label %lab1
+
+lab1:
+ %tmp21 = add i32 undef, 677038203
+ br i1 undef, label %lab2, label %exit
+
+lab2:
+ indirectbr i8* undef, [label %lab1, label %lab3]
+
+lab3:
+; CHECK: %tmp21.lcssa1 = phi i32 [ %tmp21.lcssa1, %lab4 ], [ %tmp21, %lab2 ]
+ %tmp12 = phi i32 [ %tmp21, %lab2 ], [ %tmp12, %lab4 ]
+ br i1 undef, label %lab5, label %lab4
+
+lab4:
+ br label %lab3
+
+lab5:
+; CHECK: %tmp21.lcssa1.lcssa = phi i32 [ %tmp21.lcssa1, %lab3 ]
+ %tmp15 = add i32 %tmp12, undef
+ br label %exit
+
+exit:
+ ret void
+}
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