[llvm] r179458 - Fix a scalability issue with complex ConstantExprs.
Benjamin Kramer
benny.kra at googlemail.com
Sat Apr 13 05:53:19 PDT 2013
Author: d0k
Date: Sat Apr 13 07:53:18 2013
New Revision: 179458
URL: http://llvm.org/viewvc/llvm-project?rev=179458&view=rev
Log:
Fix a scalability issue with complex ConstantExprs.
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.
Added:
llvm/trunk/test/Transforms/GlobalDCE/complex-constantexpr.ll
Modified:
llvm/trunk/lib/Analysis/ConstantFolding.cpp
llvm/trunk/lib/IR/Constants.cpp
llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp
Modified: llvm/trunk/lib/Analysis/ConstantFolding.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ConstantFolding.cpp?rev=179458&r1=179457&r2=179458&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ConstantFolding.cpp (original)
+++ llvm/trunk/lib/Analysis/ConstantFolding.cpp Sat Apr 13 07:53:18 2013
@@ -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(
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::ConstantFoldConstantExpr
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
Modified: llvm/trunk/lib/IR/Constants.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Constants.cpp?rev=179458&r1=179457&r2=179458&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Constants.cpp (original)
+++ llvm/trunk/lib/IR/Constants.cpp Sat Apr 13 07:53:18 2013
@@ -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;
Modified: llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp?rev=179458&r1=179457&r2=179458&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp Sat Apr 13 07:53:18 2013
@@ -42,6 +42,7 @@ namespace {
private:
SmallPtrSet<GlobalValue*, 32> AliveGlobals;
+ SmallPtrSet<Constant *, 8> SeenConstants;
/// GlobalIsNeeded - mark the specific global value as needed, and
/// recursively mark anything that it uses as also needed.
@@ -151,6 +152,7 @@ bool GlobalDCE::runOnModule(Module &M) {
// Make sure that all memory is released
AliveGlobals.clear();
+ SeenConstants.clear();
return Changed;
}
@@ -190,12 +192,15 @@ void GlobalDCE::GlobalIsNeeded(GlobalVal
void GlobalDCE::MarkUsedGlobalsAsNeeded(Constant *C) {
if (GlobalValue *GV = dyn_cast<GlobalValue>(C))
return GlobalIsNeeded(GV);
-
+
// Loop over all of the operands of the constant, adding any globals they
// use to the list of needed globals.
- for (User::op_iterator I = C->op_begin(), E = C->op_end(); I != E; ++I)
- if (Constant *OpC = dyn_cast<Constant>(*I))
- MarkUsedGlobalsAsNeeded(OpC);
+ for (User::op_iterator I = C->op_begin(), E = C->op_end(); I != E; ++I) {
+ // If we've already processed this constant there's no need to do it again.
+ Constant *Op = cast<Constant>(*I);
+ if (SeenConstants.insert(Op))
+ MarkUsedGlobalsAsNeeded(Op);
+ }
}
// RemoveUnusedGlobalValue - Loop over all of the uses of the specified
Added: llvm/trunk/test/Transforms/GlobalDCE/complex-constantexpr.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GlobalDCE/complex-constantexpr.ll?rev=179458&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/GlobalDCE/complex-constantexpr.ll (added)
+++ llvm/trunk/test/Transforms/GlobalDCE/complex-constantexpr.ll Sat Apr 13 07:53:18 2013
@@ -0,0 +1,97 @@
+; RUN: opt -O2 -disable-output < %s
+; PR15714
+
+%struct.ham = type { i32 }
+
+ at global5 = common global i32 0, align 4
+ at global6 = common global i32 0, align 4
+ at global7 = common global i32 0, align 4
+ at global = common global i32 0, align 4
+ at global8 = common global %struct.ham zeroinitializer, align 4
+ at global9 = common global i32 0, align 4
+ at global10 = common global i32 0, align 4
+ at global11 = common global i32 0, align 4
+
+define void @zot12() {
+bb:
+ store i32 0, i32* @global5, align 4
+ store i32 0, i32* @global6, align 4
+ br label %bb2
+
+bb1: ; preds = %bb11
+ %tmp = load i32* @global5, align 4
+ br label %bb2
+
+bb2: ; preds = %bb1, %bb
+ %tmp3 = phi i32 [ %tmp, %bb1 ], [ 0, %bb ]
+ %tmp4 = xor i32 %tmp3, zext (i1 icmp ne (i64 ptrtoint (i32* @global5 to i64), i64 1) to i32)
+ store i32 %tmp4, i32* @global5, align 4
+ %tmp5 = icmp eq i32 %tmp3, zext (i1 icmp ne (i64 ptrtoint (i32* @global5 to i64), i64 1) to i32)
+ br i1 %tmp5, label %bb8, label %bb6
+
+bb6: ; preds = %bb2
+ %tmp7 = tail call i32 @quux13()
+ br label %bb8
+
+bb8: ; preds = %bb6, %bb2
+ %tmp9 = load i32* @global7, align 4
+ %tmp10 = icmp eq i32 %tmp9, 0
+ br i1 %tmp10, label %bb11, label %bb15
+
+bb11: ; preds = %bb8
+ %tmp12 = load i32* @global6, align 4
+ %tmp13 = add nsw i32 %tmp12, 1
+ store i32 %tmp13, i32* @global6, align 4
+ %tmp14 = icmp slt i32 %tmp13, 42
+ br i1 %tmp14, label %bb1, label %bb15
+
+bb15: ; preds = %bb11, %bb8
+ ret void
+}
+
+define i32 @quux13() {
+bb:
+ store i32 1, i32* @global5, align 4
+ ret i32 1
+}
+
+define void @wombat() {
+bb:
+ tail call void @zot12()
+ ret void
+}
+
+define void @wombat14() {
+bb:
+ tail call void @blam()
+ ret void
+}
+
+define void @blam() {
+bb:
+ store i32 ptrtoint (i32* @global to i32), i32* getelementptr inbounds (%struct.ham* @global8, i64 0, i32 0), align 4
+ store i32 0, i32* @global9, align 4
+ %tmp = load i32* getelementptr inbounds (%struct.ham* @global8, i64 0, i32 0), align 4
+ br label %bb1
+
+bb1: ; preds = %bb1, %bb
+ %tmp2 = phi i32 [ 0, %bb ], [ %tmp11, %bb1 ]
+ %tmp3 = phi i32 [ %tmp, %bb ], [ %tmp10, %bb1 ]
+ %tmp4 = icmp sgt i32 %tmp3, 0
+ %tmp5 = zext i1 %tmp4 to i32
+ %tmp6 = urem i32 %tmp5, 5
+ %tmp7 = mul i32 %tmp3, -80
+ %tmp8 = or i32 %tmp7, %tmp6
+ %tmp9 = icmp eq i32 %tmp8, 0
+ %tmp10 = zext i1 %tmp9 to i32
+ %tmp11 = add nsw i32 %tmp2, 1
+ %tmp12 = icmp eq i32 %tmp11, 20
+ br i1 %tmp12, label %bb13, label %bb1
+
+bb13: ; preds = %bb1
+ store i32 %tmp10, i32* getelementptr inbounds (%struct.ham* @global8, i64 0, i32 0), align 4
+ store i32 0, i32* @global10, align 4
+ store i32 %tmp6, i32* @global11, align 4
+ store i32 20, i32* @global9, align 4
+ ret void
+}
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