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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
Download Patch File Download Diff File Expand all files Collapse all files
lib/IR/Constants.cpp
+19 -9
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@@ -237,18 +237,21 @@ void Constant::destroyConstantImpl() {
delete this;
}
/// canTrap - Return true if evaluation of this constant could trap. This is
/// true for things like constant expressions that could divide by zero.
bool Constant::canTrap() const {
assert(getType()->isFirstClassType() && "Cannot evaluate aggregate vals!");
static bool canTrapImpl(const Constant *C,
SmallPtrSet<const ConstantExpr *, 4> &NonTrappingOps) {
assert(C->getType()->isFirstClassType() && "Cannot evaluate aggregate vals!");
// The only thing that could possibly trap are constant exprs.
const ConstantExpr *CE = dyn_cast<ConstantExpr>(this);
if (!CE) return false;
const ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
if (!CE)
return false;
// ConstantExpr traps if any operands can trap.
for (unsigned i = 0, e = getNumOperands(); i != e; ++i)
if (CE->getOperand(i)->canTrap())
return true;
for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) {
if (ConstantExpr *Op = dyn_cast<ConstantExpr>(CE->getOperand(i))) {
if (NonTrappingOps.insert(Op) && canTrapImpl(Op, NonTrappingOps))
return true;
}
}
// Otherwise, only specific operations can trap.
switch (CE->getOpcode()) {
@@ -267,6 +270,13 @@ bool Constant::canTrap() const {
}
}
/// canTrap - Return true if evaluation of this constant could trap. This is
/// true for things like constant expressions that could divide by zero.
bool Constant::canTrap() const {
SmallPtrSet<const ConstantExpr *, 4> NonTrappingOps;
return canTrapImpl(this, NonTrappingOps);
}
/// isThreadDependent - Return true if the value can vary between threads.
bool Constant::isThreadDependent() const {
SmallPtrSet<const Constant*, 64> Visited;