[llvm] r249712 - [SCEV] Pick backedge values for phi nodes correctly
Sanjoy Das via llvm-commits
llvm-commits at lists.llvm.org
Thu Oct 8 11:28:38 PDT 2015
Author: sanjoy
Date: Thu Oct 8 13:28:36 2015
New Revision: 249712
URL: http://llvm.org/viewvc/llvm-project?rev=249712&view=rev
Log:
[SCEV] Pick backedge values for phi nodes correctly
Summary:
`getConstantEvolutionLoopExitValue` and `ComputeExitCountExhaustively`
assumed all phi nodes in the loop header have the same order of incoming
values. This is not correct, and this commit changes
`getConstantEvolutionLoopExitValue` and `ComputeExitCountExhaustively`
to lookup the backedge value of a phi node using the loop's latch block.
Unfortunately, there is still some code duplication
`getConstantEvolutionLoopExitValue` and `ComputeExitCountExhaustively`.
At some point in the future we should extract out a helper class /
method that can evolve constant evolution phi nodes across iterations.
Fixes 25060. Thanks to Mattias Eriksson for the spot-on analysis!
Depends on D13457.
Reviewers: atrick, hfinkel
Subscribers: materi, llvm-commits
Differential Revision: http://reviews.llvm.org/D13458
Added:
llvm/trunk/test/Transforms/IndVarSimplify/pr25060.ll
Modified:
llvm/trunk/lib/Analysis/ScalarEvolution.cpp
Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=249712&r1=249711&r2=249712&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Thu Oct 8 13:28:36 2015
@@ -5742,22 +5742,36 @@ ScalarEvolution::getConstantEvolutionLoo
BasicBlock *Header = L->getHeader();
assert(PN->getParent() == Header && "Can't evaluate PHI not in loop header!");
- // Since the loop is canonicalized, the PHI node must have two entries. One
+ BasicBlock *Latch = L->getLoopLatch();
+ if (!Latch)
+ return nullptr;
+
+ // Since the loop has one latch, the PHI node must have two entries. One
// entry must be a constant (coming in from outside of the loop), and the
// second must be derived from the same PHI.
- bool SecondIsBackedge = L->contains(PN->getIncomingBlock(1));
+
+ BasicBlock *NonLatch = Latch == PN->getIncomingBlock(0)
+ ? PN->getIncomingBlock(1)
+ : PN->getIncomingBlock(0);
+
+ assert(PN->getNumIncomingValues() == 2 && "Follows from having one latch!");
+
+ // Note: not all PHI nodes in the same block have to have their incoming
+ // values in the same order, so we use the basic block to look up the incoming
+ // value, not an index.
+
for (auto &I : *Header) {
PHINode *PHI = dyn_cast<PHINode>(&I);
if (!PHI) break;
auto *StartCST =
- dyn_cast<Constant>(PHI->getIncomingValue(!SecondIsBackedge));
+ dyn_cast<Constant>(PHI->getIncomingValueForBlock(NonLatch));
if (!StartCST) continue;
CurrentIterVals[PHI] = StartCST;
}
if (!CurrentIterVals.count(PN))
return RetVal = nullptr;
- Value *BEValue = PN->getIncomingValue(SecondIsBackedge);
+ Value *BEValue = PN->getIncomingValueForBlock(Latch);
// Execute the loop symbolically to determine the exit value.
if (BEs.getActiveBits() >= 32)
@@ -5796,7 +5810,7 @@ ScalarEvolution::getConstantEvolutionLoo
PHINode *PHI = I.first;
Constant *&NextPHI = NextIterVals[PHI];
if (!NextPHI) { // Not already computed.
- Value *BEValue = PHI->getIncomingValue(SecondIsBackedge);
+ Value *BEValue = PHI->getIncomingValueForBlock(Latch);
NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, DL, &TLI);
}
if (NextPHI != I.second)
@@ -5831,15 +5845,24 @@ const SCEV *ScalarEvolution::ComputeExit
BasicBlock *Header = L->getHeader();
assert(PN->getParent() == Header && "Can't evaluate PHI not in loop header!");
- // One entry must be a constant (coming in from outside of the loop), and the
- // second must be derived from the same PHI.
- bool SecondIsBackedge = L->contains(PN->getIncomingBlock(1));
+ BasicBlock *Latch = L->getLoopLatch();
+ assert(Latch && "Should follow from NumIncomingValues == 2!");
+
+ // NonLatch is the preheader, or something equivalent.
+ BasicBlock *NonLatch = Latch == PN->getIncomingBlock(0)
+ ? PN->getIncomingBlock(1)
+ : PN->getIncomingBlock(0);
+
+ // Note: not all PHI nodes in the same block have to have their incoming
+ // values in the same order, so we use the basic block to look up the incoming
+ // value, not an index.
+
for (auto &I : *Header) {
PHINode *PHI = dyn_cast<PHINode>(&I);
if (!PHI)
break;
auto *StartCST =
- dyn_cast<Constant>(PHI->getIncomingValue(!SecondIsBackedge));
+ dyn_cast<Constant>(PHI->getIncomingValueForBlock(NonLatch));
if (!StartCST) continue;
CurrentIterVals[PHI] = StartCST;
}
@@ -5879,7 +5902,7 @@ const SCEV *ScalarEvolution::ComputeExit
Constant *&NextPHI = NextIterVals[PHI];
if (NextPHI) continue; // Already computed!
- Value *BEValue = PHI->getIncomingValue(SecondIsBackedge);
+ Value *BEValue = PHI->getIncomingValueForBlock(Latch);
NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, DL, &TLI);
}
CurrentIterVals.swap(NextIterVals);
Added: llvm/trunk/test/Transforms/IndVarSimplify/pr25060.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/pr25060.ll?rev=249712&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/IndVarSimplify/pr25060.ll (added)
+++ llvm/trunk/test/Transforms/IndVarSimplify/pr25060.ll Thu Oct 8 13:28:36 2015
@@ -0,0 +1,37 @@
+; RUN: opt -S -indvars < %s | FileCheck %s
+
+define i16 @fn1() {
+; CHECK-LABEL: @fn1(
+entry:
+ br label %bb1
+
+bb1:
+ %i = phi i16 [ 0, %entry ], [ 1, %bb1 ]
+ %storemerge = phi i16 [ %storemerge2, %bb1 ], [ 0, %entry ]
+ %storemerge2 = phi i16 [ 10, %entry ], [ 200, %bb1 ]
+ %tmp10 = icmp eq i16 %i, 1
+ br i1 %tmp10, label %bb5, label %bb1
+
+bb5:
+ %storemerge.lcssa = phi i16 [ %storemerge, %bb1 ]
+; CHECK: ret i16 10
+ ret i16 %storemerge.lcssa
+}
+
+define i16 @fn2() {
+; CHECK-LABEL: @fn2(
+entry:
+ br label %bb1
+
+bb1:
+ %canary = phi i16 [ 0, %entry ], [ %canary.inc, %bb1 ]
+ %i = phi i16 [ 0, %entry ], [ %storemerge, %bb1 ]
+ %storemerge = phi i16 [ 0, %bb1 ], [ 10, %entry ]
+ %canary.inc = add i16 %canary, 1
+ %_tmp10 = icmp eq i16 %i, 10
+ br i1 %_tmp10, label %bb5, label %bb1
+
+bb5:
+; CHECK: ret i16 1
+ ret i16 %canary
+}
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