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Reapply r142781 with fix. Original message:

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Enhance SCEV's brute force loop analysis to handle multiple PHI nodes in the
  loop header when computing the trip count.

  With this, we now constant evaluate:
    struct ListNode { const struct ListNode *next; int i; };
    static const struct ListNode node1 = {0, 1};
    static const struct ListNode node2 = {&node1, 2};
    static const struct ListNode node3 = {&node2, 3};
    int test() {
      int sum = 0;
      for (const struct ListNode *n = &node3; n != 0; n = n->next)
        sum += n->i;
      return sum;
    }


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142790 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2011-10-24 06:57:05 +00:00
parent f46c674a16
commit 7c3fc57472
2 changed files with 65 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

52
lib/Analysis/ScalarEvolution.cpp
View File

@ -4882,29 +4882,33 @@ const SCEV *ScalarEvolution::ComputeExitCountExhaustively(const Loop *L,
// That's the only form we support here.
if (PN->getNumIncomingValues() != 2) return getCouldNotCompute();
DenseMap<Instruction *, Constant *> CurrentIterVals;
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));
Constant *StartCST =
dyn_cast<Constant>(PN->getIncomingValue(!SecondIsBackedge));
if (StartCST == 0) return getCouldNotCompute(); // Must be a constant.
Value *BEValue = PN->getIncomingValue(SecondIsBackedge);
if (getConstantEvolvingPHI(BEValue, L) != PN &&
!isa<Constant>(BEValue))
return getCouldNotCompute(); // Not derived from same PHI.
PHINode *PHI = 0;
for (BasicBlock::iterator I = Header->begin();
(PHI = dyn_cast<PHINode>(I)); ++I) {
Constant *StartCST =
dyn_cast<Constant>(PHI->getIncomingValue(!SecondIsBackedge));
if (StartCST == 0) continue;
CurrentIterVals[PHI] = StartCST;
}
if (!CurrentIterVals.count(PN))
return getCouldNotCompute();
// Okay, we find a PHI node that defines the trip count of this loop. Execute
// the loop symbolically to determine when the condition gets a value of
// "ExitWhen".
unsigned IterationNum = 0;
unsigned MaxIterations = MaxBruteForceIterations; // Limit analysis.
for (Constant *PHIVal = StartCST;
IterationNum != MaxIterations; ++IterationNum) {
DenseMap<Instruction *, Constant *> PHIValMap;
PHIValMap[PN] = PHIVal;
unsigned MaxIterations = MaxBruteForceIterations; // Limit analysis.
for (unsigned IterationNum = 0; IterationNum != MaxIterations;++IterationNum){
ConstantInt *CondVal =
dyn_cast_or_null<ConstantInt>(EvaluateExpression(Cond, L, PHIValMap, TD));
dyn_cast_or_null<ConstantInt>(EvaluateExpression(Cond, L,
CurrentIterVals, TD));
// Couldn't symbolically evaluate.
if (!CondVal) return getCouldNotCompute();
@ -4914,11 +4918,19 @@ const SCEV *ScalarEvolution::ComputeExitCountExhaustively(const Loop *L,
return getConstant(Type::getInt32Ty(getContext()), IterationNum);
}
// Compute the value of the PHI node for the next iteration.
Constant *NextPHI = EvaluateExpression(BEValue, L, PHIValMap, TD);
if (NextPHI == 0 || NextPHI == PHIVal)
return getCouldNotCompute();// Couldn't evaluate or not making progress...
PHIVal = NextPHI;
// Update all the PHI nodes for the next iteration.
DenseMap<Instruction *, Constant *> NextIterVals;
for (DenseMap<Instruction *, Constant *>::const_iterator
I = CurrentIterVals.begin(), E = CurrentIterVals.end(); I != E; ++I){
PHINode *PHI = dyn_cast<PHINode>(I->first);
if (!PHI || PHI->getParent() != Header) continue;
Constant *&NextPHI = NextIterVals[PHI];
if (NextPHI) continue; // Already computed!
Value *BEValue = PHI->getIncomingValue(SecondIsBackedge);
NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, TD);
}
CurrentIterVals.swap(NextIterVals);
}
// Too many iterations were needed to evaluate.

34
test/Analysis/ScalarEvolution/load.ll
View File

@ -1,5 +1,4 @@
; RUN: opt -analyze -scalar-evolution < %s 2>&1 | FileCheck %s
; PR11034
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32"
target triple = "i386-pc-linux-gnu"
@ -7,6 +6,7 @@ target triple = "i386-pc-linux-gnu"
@arr1 = internal unnamed_addr constant [50 x i32] [i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 16, i32 17, i32 18, i32 19, i32 20, i32 21, i32 22, i32 23, i32 24, i32 25, i32 26, i32 27, i32 28, i32 29, i32 30, i32 31, i32 32, i32 33, i32 34, i32 35, i32 36, i32 37, i32 38, i32 39, i32 40, i32 41, i32 42, i32 43, i32 44, i32 45, i32 46, i32 47, i32 48, i32 49, i32 50], align 4
@arr2 = internal unnamed_addr constant [50 x i32] [i32 49, i32 48, i32 47, i32 46, i32 45, i32 44, i32 43, i32 42, i32 41, i32 40, i32 39, i32 38, i32 37, i32 36, i32 35, i32 34, i32 33, i32 32, i32 31, i32 30, i32 29, i32 28, i32 27, i32 26, i32 25, i32 24, i32 23, i32 22, i32 21, i32 20, i32 19, i32 18, i32 17, i32 16, i32 15, i32 14, i32 13, i32 12, i32 11, i32 10, i32 9, i32 8, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0], align 4
; PR11034
define i32 @test1() nounwind readnone {
; CHECK: test1
entry:
@ -31,3 +31,35 @@ for.body: ; preds = %entry, %for.body
for.end: ; preds = %for.body
ret i32 %add2
}
%struct.ListNode = type { %struct.ListNode*, i32 }
@node5 = internal constant { %struct.ListNode*, i32, [4 x i8] } { %struct.ListNode* bitcast ({ %struct.ListNode*, i32, [4 x i8] }* @node4 to %struct.ListNode*), i32 4, [4 x i8] undef }, align 8
@node4 = internal constant { %struct.ListNode*, i32, [4 x i8] } { %struct.ListNode* bitcast ({ %struct.ListNode*, i32, [4 x i8] }* @node3 to %struct.ListNode*), i32 3, [4 x i8] undef }, align 8
@node3 = internal constant { %struct.ListNode*, i32, [4 x i8] } { %struct.ListNode* bitcast ({ %struct.ListNode*, i32, [4 x i8] }* @node2 to %struct.ListNode*), i32 2, [4 x i8] undef }, align 8
@node2 = internal constant { %struct.ListNode*, i32, [4 x i8] } { %struct.ListNode* bitcast ({ %struct.ListNode*, i32, [4 x i8] }* @node1 to %struct.ListNode*), i32 1, [4 x i8] undef }, align 8
@node1 = internal constant { %struct.ListNode*, i32, [4 x i8] } { %struct.ListNode* null, i32 0, [4 x i8] undef }, align 8
define i32 @test2() nounwind uwtable readonly {
; CHECK: test2
entry:
br label %for.body
for.body: ; preds = %entry, %for.body
%sum.02 = phi i32 [ 0, %entry ], [ %add, %for.body ]
; CHECK: --> %sum.02{{ *}}Exits: 10
%n.01 = phi %struct.ListNode* [ bitcast ({ %struct.ListNode*, i32, [4 x i8] }* @node5 to %struct.ListNode*), %entry ], [ %1, %for.body ]
; CHECK: --> %n.01{{ *}}Exits: @node1
%i = getelementptr inbounds %struct.ListNode* %n.01, i64 0, i32 1
%0 = load i32* %i, align 4
%add = add nsw i32 %0, %sum.02
%next = getelementptr inbounds %struct.ListNode* %n.01, i64 0, i32 0
%1 = load %struct.ListNode** %next, align 8
; CHECK: --> %1{{ *}}Exits: 0
%cmp = icmp eq %struct.ListNode* %1, null
br i1 %cmp, label %for.end, label %for.body
for.end: ; preds = %for.body
ret i32 %add
}