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[SCEV] Fix PR25369 

Have `getConstantEvolutionLoopExitValue` work correctly with multiple
entry loops.

As far as I can tell, `getConstantEvolutionLoopExitValue` never did the
right thing for multiple entry loops; and before r249712 it would
silently return an incorrect answer.  r249712 changed SCEV to fail an
assert on a multiple entry loop, and this change fixes the underlying
issue.

llvm-svn: 251770
This commit is contained in:
Sanjoy Das 2015-11-02 02:06:01 +00:00
parent 50df0c2037
commit 52bfa0faa4
2 changed files with 104 additions and 27 deletions
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53
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -5928,6 +5928,30 @@ static Constant *EvaluateExpression(Value *V, const Loop *L,
TLI);
}
// If every incoming value to PN except the one for BB is a specific Constant,
// return that, else return nullptr.
static Constant *getOtherIncomingValue(PHINode *PN, BasicBlock *BB) {
Constant *IncomingVal = nullptr;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
if (PN->getIncomingBlock(i) == BB)
continue;
auto *CurrentVal = dyn_cast<Constant>(PN->getIncomingValue(i));
if (!CurrentVal)
return nullptr;
if (IncomingVal != CurrentVal) {
if (IncomingVal)
return nullptr;
IncomingVal = CurrentVal;
}
}
return IncomingVal;
}
/// getConstantEvolutionLoopExitValue - If we know that the specified Phi is
/// in the header of its containing loop, we know the loop executes a
/// constant number of times, and the PHI node is just a recurrence
@ -5953,25 +5977,10 @@ ScalarEvolution::getConstantEvolutionLoopExitValue(PHINode *PN,
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.
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->getIncomingValueForBlock(NonLatch));
auto *StartCST = getOtherIncomingValue(PHI, Latch);
if (!StartCST) continue;
CurrentIterVals[PHI] = StartCST;
}
@ -6050,21 +6059,11 @@ const SCEV *ScalarEvolution::computeExitCountExhaustively(const Loop *L,
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->getIncomingValueForBlock(NonLatch));
auto *StartCST = getOtherIncomingValue(PHI, Latch);
if (!StartCST) continue;
CurrentIterVals[PHI] = StartCST;
}

78
llvm/test/Analysis/ScalarEvolution/pr25369.ll Normal file
View File

@ -0,0 +1,78 @@
; RUN: opt -analyze -scalar-evolution < %s | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
define void @hoge1() {
; CHECK-LABEL: Classifying expressions for: @hoge1
bb:
br i1 undef, label %bb4, label %bb2
bb2: ; preds = %bb2, %bb
br i1 false, label %bb4, label %bb2
bb3: ; preds = %bb4
%tmp = add i32 %tmp10, -1
br label %bb13
bb4: ; preds = %bb4, %bb2, %bb
%tmp5 = phi i64 [ %tmp11, %bb4 ], [ 1, %bb2 ], [ 1, %bb ]
%tmp6 = phi i32 [ %tmp10, %bb4 ], [ 0, %bb2 ], [ 0, %bb ]
%tmp7 = load i32, i32* undef, align 4
%tmp8 = add i32 %tmp7, %tmp6
%tmp9 = add i32 undef, %tmp8
%tmp10 = add i32 undef, %tmp9
%tmp11 = add nsw i64 %tmp5, 3
%tmp12 = icmp eq i64 %tmp11, 64
br i1 %tmp12, label %bb3, label %bb4
; CHECK: Loop %bb4: backedge-taken count is 20
; CHECK: Loop %bb4: max backedge-taken count is 20
bb13: ; preds = %bb13, %bb3
%tmp14 = phi i64 [ 0, %bb3 ], [ %tmp15, %bb13 ]
%tmp15 = add nuw nsw i64 %tmp14, 1
%tmp16 = trunc i64 %tmp15 to i32
%tmp17 = icmp eq i32 %tmp16, %tmp
br i1 %tmp17, label %bb18, label %bb13
bb18: ; preds = %bb13
ret void
}
define void @hoge2() {
; CHECK-LABEL: Classifying expressions for: @hoge2
bb:
br i1 undef, label %bb4, label %bb2
bb2: ; preds = %bb2, %bb
br i1 false, label %bb4, label %bb2
bb3: ; preds = %bb4
%tmp = add i32 %tmp10, -1
br label %bb13
bb4: ; preds = %bb4, %bb2, %bb
%tmp5 = phi i64 [ %tmp11, %bb4 ], [ 1, %bb2 ], [ 3, %bb ]
%tmp6 = phi i32 [ %tmp10, %bb4 ], [ 0, %bb2 ], [ 0, %bb ]
%tmp7 = load i32, i32* undef, align 4
%tmp8 = add i32 %tmp7, %tmp6
%tmp9 = add i32 undef, %tmp8
%tmp10 = add i32 undef, %tmp9
%tmp11 = add nsw i64 %tmp5, 3
%tmp12 = icmp eq i64 %tmp11, 64
br i1 %tmp12, label %bb3, label %bb4
; CHECK: Loop %bb4: Unpredictable backedge-taken count.
; CHECK: Loop %bb4: Unpredictable max backedge-taken count.
bb13: ; preds = %bb13, %bb3
%tmp14 = phi i64 [ 0, %bb3 ], [ %tmp15, %bb13 ]
%tmp15 = add nuw nsw i64 %tmp14, 1
%tmp16 = trunc i64 %tmp15 to i32
%tmp17 = icmp eq i32 %tmp16, %tmp
br i1 %tmp17, label %bb18, label %bb13
bb18: ; preds = %bb13
ret void
}