[llvm] r284311 - [GVN/PRE] Hoist global values outside of loops.
Davide Italiano via llvm-commits
llvm-commits at lists.llvm.org
Sat Oct 15 14:35:23 PDT 2016
Author: davide
Date: Sat Oct 15 16:35:23 2016
New Revision: 284311
URL: http://llvm.org/viewvc/llvm-project?rev=284311&view=rev
Log:
[GVN/PRE] Hoist global values outside of loops.
In theory this could be generalized to move anything where
we prove the operands are available, but that would require
rewriting PRE. As NewGVN will hopefully come soon, and we're
trying to rewrite PRE in terms of NewGVN+MemorySSA, it's probably
not worth spending too much time on it. Fix provided by
Daniel Berlin!
Added:
llvm/trunk/test/Transforms/GVN/PRE/hoist-loads.ll
Modified:
llvm/trunk/lib/Transforms/Scalar/GVN.cpp
llvm/trunk/test/Transforms/GVN/PRE/pre-single-pred.ll
Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVN.cpp?rev=284311&r1=284310&r2=284311&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Sat Oct 15 16:35:23 2016
@@ -122,69 +122,84 @@ template <> struct DenseMapInfo<GVN::Exp
/// location of the instruction from which it was formed.
struct llvm::gvn::AvailableValue {
enum ValType {
- SimpleVal, // A simple offsetted value that is accessed.
- LoadVal, // A value produced by a load.
- MemIntrin, // A memory intrinsic which is loaded from.
- UndefVal // A UndefValue representing a value from dead block (which
- // is not yet physically removed from the CFG).
+ SimpleVal, // A simple offsetted value that is accessed.
+ LoadVal, // A value produced by a load.
+ MemIntrinVal, // A memory intrinsic which is loaded from.
+ UndefVal, // A UndefValue representing a value from dead block (which
+ // is not yet physically removed from the CFG).
+ CreateLoadVal // A duplicate load can be created higher up in the CFG that
+ // will eliminate this one.
};
/// V - The value that is live out of the block.
- PointerIntPair<Value *, 2, ValType> Val;
+ std::pair<Value *, ValType> Val;
/// Offset - The byte offset in Val that is interesting for the load query.
unsigned Offset;
static AvailableValue get(Value *V, unsigned Offset = 0) {
AvailableValue Res;
- Res.Val.setPointer(V);
- Res.Val.setInt(SimpleVal);
+ Res.Val.first = V;
+ Res.Val.second = SimpleVal;
Res.Offset = Offset;
return Res;
}
static AvailableValue getMI(MemIntrinsic *MI, unsigned Offset = 0) {
AvailableValue Res;
- Res.Val.setPointer(MI);
- Res.Val.setInt(MemIntrin);
+ Res.Val.first = MI;
+ Res.Val.second = MemIntrinVal;
Res.Offset = Offset;
return Res;
}
+ static AvailableValue getCreateLoad(LoadInst *LI) {
+ AvailableValue Res;
+ Res.Val.first = LI;
+ Res.Val.second = CreateLoadVal;
+ return Res;
+ }
+
static AvailableValue getLoad(LoadInst *LI, unsigned Offset = 0) {
AvailableValue Res;
- Res.Val.setPointer(LI);
- Res.Val.setInt(LoadVal);
+ Res.Val.first = LI;
+ Res.Val.second = LoadVal;
Res.Offset = Offset;
return Res;
}
static AvailableValue getUndef() {
AvailableValue Res;
- Res.Val.setPointer(nullptr);
- Res.Val.setInt(UndefVal);
+ Res.Val.first = nullptr;
+ Res.Val.second = UndefVal;
Res.Offset = 0;
return Res;
}
- bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
- bool isCoercedLoadValue() const { return Val.getInt() == LoadVal; }
- bool isMemIntrinValue() const { return Val.getInt() == MemIntrin; }
- bool isUndefValue() const { return Val.getInt() == UndefVal; }
+ bool isSimpleValue() const { return Val.second == SimpleVal; }
+ bool isCoercedLoadValue() const { return Val.second == LoadVal; }
+ bool isMemIntrinValue() const { return Val.second == MemIntrinVal; }
+ bool isUndefValue() const { return Val.second == UndefVal; }
+ bool isCreateLoadValue() const { return Val.second == CreateLoadVal; }
+
+ LoadInst *getCreateLoadValue() const {
+ assert(isCreateLoadValue() && "Wrong accessor");
+ return cast<LoadInst>(Val.first);
+ }
Value *getSimpleValue() const {
assert(isSimpleValue() && "Wrong accessor");
- return Val.getPointer();
+ return Val.first;
}
LoadInst *getCoercedLoadValue() const {
assert(isCoercedLoadValue() && "Wrong accessor");
- return cast<LoadInst>(Val.getPointer());
+ return cast<LoadInst>(Val.first);
}
MemIntrinsic *getMemIntrinValue() const {
assert(isMemIntrinValue() && "Wrong accessor");
- return cast<MemIntrinsic>(Val.getPointer());
+ return cast<MemIntrinsic>(Val.first);
}
/// Emit code at the specified insertion point to adjust the value defined
@@ -1191,7 +1206,11 @@ Value *AvailableValue::MaterializeAdjust
Value *Res;
Type *LoadTy = LI->getType();
const DataLayout &DL = LI->getModule()->getDataLayout();
- if (isSimpleValue()) {
+ if (isCreateLoadValue()) {
+ Instruction *I = getCreateLoadValue()->clone();
+ I->insertBefore(InsertPt);
+ Res = I;
+ } else if (isSimpleValue()) {
Res = getSimpleValue();
if (Res->getType() != LoadTy) {
Res = GetStoreValueForLoad(Res, Offset, LoadTy, InsertPt, DL);
@@ -1379,7 +1398,7 @@ void GVN::AnalyzeLoadAvailability(LoadIn
continue;
}
- if (!DepInfo.isDef() && !DepInfo.isClobber()) {
+ if (!DepInfo.isDef() && !DepInfo.isClobber() && !DepInfo.isNonFuncLocal()) {
UnavailableBlocks.push_back(DepBB);
continue;
}
@@ -1390,12 +1409,25 @@ void GVN::AnalyzeLoadAvailability(LoadIn
Value *Address = Deps[i].getAddress();
AvailableValue AV;
- if (AnalyzeLoadAvailability(LI, DepInfo, Address, AV)) {
+ // TODO: We can use anything where the operands are available, and we should
+ // learn to recreate operands in other blocks if they are available.
+ // Because we don't have the infrastructure in our PRE, we restrict this to
+ // global values, because we know the operands are always available.
+ if (DepInfo.isNonFuncLocal()) {
+ if (isSafeToSpeculativelyExecute(LI) &&
+ isa<GlobalValue>(LI->getPointerOperand())) {
+ AV = AvailableValue::getCreateLoad(LI);
+ ValuesPerBlock.push_back(AvailableValueInBlock::get(
+ &LI->getParent()->getParent()->getEntryBlock(), std::move(AV)));
+ } else
+ UnavailableBlocks.push_back(DepBB);
+
+ } else if (AnalyzeLoadAvailability(LI, DepInfo, Address, AV)) {
// subtlety: because we know this was a non-local dependency, we know
// it's safe to materialize anywhere between the instruction within
// DepInfo and the end of it's block.
- ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
- std::move(AV)));
+ ValuesPerBlock.push_back(
+ AvailableValueInBlock::get(DepBB, std::move(AV)));
} else {
UnavailableBlocks.push_back(DepBB);
}
Added: llvm/trunk/test/Transforms/GVN/PRE/hoist-loads.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GVN/PRE/hoist-loads.ll?rev=284311&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/GVN/PRE/hoist-loads.ll (added)
+++ llvm/trunk/test/Transforms/GVN/PRE/hoist-loads.ll Sat Oct 15 16:35:23 2016
@@ -0,0 +1,53 @@
+; RUN: opt -gvn %s -S -o - | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Check that the loads of @aaa, @bbb and @ccc are hoisted.
+; CHECK-LABEL: define void @foo
+; CHECK-NEXT: %2 = load i32, i32* @ccc, align 4
+; CHECK-NEXT: %3 = load i32, i32* @bbb, align 4
+; CHECK-NEXT: %4 = load i32, i32* @aaa, align 4
+
+ at aaa = local_unnamed_addr global i32 10, align 4
+ at bbb = local_unnamed_addr global i32 20, align 4
+ at ccc = local_unnamed_addr global i32 30, align 4
+
+define void @foo(i32* nocapture readonly) local_unnamed_addr {
+ br label %2
+
+ %.0 = phi i32* [ %0, %1 ], [ %3, %22 ]
+ %3 = getelementptr inbounds i32, i32* %.0, i64 1
+ %4 = load i32, i32* %.0, align 4
+ %5 = load i32, i32* @ccc, align 4
+ %6 = icmp sgt i32 %4, %5
+ br i1 %6, label %7, label %10
+
+ %8 = load i32, i32* @bbb, align 4
+ %9 = add nsw i32 %8, %4
+ store i32 %9, i32* @bbb, align 4
+ br label %10
+
+ %11 = load i32, i32* @bbb, align 4
+ %12 = icmp sgt i32 %4, %11
+ br i1 %12, label %13, label %16
+
+ %14 = load i32, i32* @aaa, align 4
+ %15 = add nsw i32 %14, %4
+ store i32 %15, i32* @aaa, align 4
+ br label %16
+
+ %17 = load i32, i32* @aaa, align 4
+ %18 = icmp sgt i32 %4, %17
+ br i1 %18, label %19, label %22
+
+ %20 = load i32, i32* @ccc, align 4
+ %21 = add nsw i32 %20, %4
+ store i32 %21, i32* @ccc, align 4
+ br label %22
+
+ %23 = icmp slt i32 %4, 0
+ br i1 %23, label %24, label %2
+
+ ret void
+}
Modified: llvm/trunk/test/Transforms/GVN/PRE/pre-single-pred.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GVN/PRE/pre-single-pred.ll?rev=284311&r1=284310&r2=284311&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/GVN/PRE/pre-single-pred.ll (original)
+++ llvm/trunk/test/Transforms/GVN/PRE/pre-single-pred.ll Sat Oct 15 16:35:23 2016
@@ -1,16 +1,9 @@
; RUN: opt < %s -gvn -enable-load-pre -S | FileCheck %s
-; This testcase assumed we'll PRE the load into %for.cond, but we don't actually
-; verify that doing so is safe. If there didn't _happen_ to be a load in
-; %for.end, we would actually be lengthening the execution on some paths, and
-; we were never actually checking that case. Now we actually do perform some
-; conservative checking to make sure we don't make paths longer, but we don't
-; currently get this case, which we got lucky on previously.
-;
-; Now that that faulty assumption is corrected, test that we DON'T incorrectly
-; hoist the load. Doing the right thing for the wrong reasons is still a bug.
@p = external global i32
define i32 @f(i32 %n) nounwind {
+; CHECK: entry:
+; CHECK-NEXT: %0 = load i32, i32* @p
entry:
br label %for.cond
@@ -22,8 +15,9 @@ for.cond: ; preds = %for.inc, %entry
for.cond.for.end_crit_edge: ; preds = %for.cond
br label %for.end
+; The load of @p should be hoisted into the entry block.
; CHECK: for.body:
-; CHECK-NEXT: %tmp3 = load i32, i32* @p
+; CHECK-NEXT: %dec = add i32 %tmp3, -1
for.body: ; preds = %for.cond
%tmp3 = load i32, i32* @p ; <i32> [#uses=1]
%dec = add i32 %tmp3, -1 ; <i32> [#uses=2]
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