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Fix a scalability issue with complex ConstantExprs.

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This is basically the same fix in three different places. We use a set to avoid
walking the whole tree of a big ConstantExprs multiple times.

For example: (select cmp, (add big_expr 1), (add big_expr 2))
We don't want to visit big_expr twice here, it may consist of thousands of
nodes.

The testcase exercises this by creating an insanely large ConstantExprs out of
a loop. It's questionable if the optimizer should ever create those, but this
can be triggered with real C code. Fixes PR15714.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179458 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer
2013-04-13 12:53:18 +00:00
parent b99c995825
commit 8848680ce0
4 changed files with 149 additions and 25 deletions
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36
lib/Analysis/ConstantFolding.cpp
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@@ -17,6 +17,7 @@
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Analysis/ValueTracking.h"
@@ -880,19 +881,20 @@ Constant *llvm::ConstantFoldInstruction(Instruction *I,
return ConstantFoldInstOperands(I->getOpcode(), I->getType(), Ops, TD, TLI);
}
/// ConstantFoldConstantExpression - Attempt to fold the constant expression
/// using the specified DataLayout. If successful, the constant result is
/// result is returned, if not, null is returned.
Constant *llvm::ConstantFoldConstantExpression(const ConstantExpr *CE,
const DataLayout *TD,
const TargetLibraryInfo *TLI) {
SmallVector<Constant*, 8> Ops;
for (User::const_op_iterator i = CE->op_begin(), e = CE->op_end();
i != e; ++i) {
static Constant *
ConstantFoldConstantExpressionImpl(const ConstantExpr *CE, const DataLayout *TD,
const TargetLibraryInfo *TLI,
SmallPtrSet<ConstantExpr *, 4> &FoldedOps) {
SmallVector<Constant *, 8> Ops;
for (User::const_op_iterator i = CE->op_begin(), e = CE->op_end(); i != e;
++i) {
Constant *NewC = cast<Constant>(*i);
// Recursively fold the ConstantExpr's operands.
if (ConstantExpr *NewCE = dyn_cast<ConstantExpr>(NewC))
NewC = ConstantFoldConstantExpression(NewCE, TD, TLI);
// Recursively fold the ConstantExpr's operands. If we have already folded
// a ConstantExpr, we don't have to process it again.
if (ConstantExpr *NewCE = dyn_cast<ConstantExpr>(NewC)) {
if (FoldedOps.insert(NewCE))
NewC = ConstantFoldConstantExpressionImpl(NewCE, TD, TLI, FoldedOps);
}
Ops.push_back(NewC);
}
@@ -902,6 +904,16 @@ Constant *llvm::ConstantFoldConstantExpression(const ConstantExpr *CE,
return ConstantFoldInstOperands(CE->getOpcode(), CE->getType(), Ops, TD, TLI);
}
/// ConstantFoldConstantExpression - Attempt to fold the constant expression
/// using the specified DataLayout. If successful, the constant result is
/// result is returned, if not, null is returned.
Constant *llvm::ConstantFoldConstantExpression(const ConstantExpr *CE,
const DataLayout *TD,
const TargetLibraryInfo *TLI) {
SmallPtrSet<ConstantExpr *, 4> FoldedOps;
return ConstantFoldConstantExpressionImpl(CE, TD, TLI, FoldedOps);
}
/// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
/// specified opcode and operands. If successful, the constant result is
/// returned, if not, null is returned. Note that this function can fail when