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Teach argpromote to ruthlessly hack small byval structs when it can

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get away with it, which exposes opportunities to eliminate the memory
objects entirely.  For example, we now compile byval.ll to:

define internal void @f1(i32 %b.0, i64 %b.1) {
entry:
	%tmp2 = add i32 %b.0, 1		; <i32> [#uses=0]
	ret void
}

define i32 @main() nounwind  {
entry:
	call void @f1( i32 1, i64 2 )
	ret i32 0
}

This seems like it would trigger a lot for code that passes around small
structs (e.g. SDOperand's or _Complex)...



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45886 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-01-11 22:31:41 +00:00
parent 8bc16f0e0e
commit 10603e0c84
2 changed files with 178 additions and 74 deletions
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122
lib/Transforms/IPO/ArgumentPromotion.cpp
View File

@ -51,6 +51,7 @@ using namespace llvm;
STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted");
STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted");
STATISTIC(NumByValArgsPromoted , "Number of byval arguments promoted");
STATISTIC(NumArgumentsDead , "Number of dead pointer args eliminated");
namespace {
@ -71,7 +72,8 @@ namespace {
bool PromoteArguments(CallGraphNode *CGN);
bool isSafeToPromoteArgument(Argument *Arg, bool isByVal) const;
Function *DoPromotion(Function *F,
SmallPtrSet<Argument*, 8> &ArgsToPromote);
SmallPtrSet<Argument*, 8> &ArgsToPromote,
SmallPtrSet<Argument*, 8> &ByValArgsToTransform);
};
char ArgPromotion::ID = 0;
@ -134,16 +136,44 @@ bool ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
// Check to see which arguments are promotable. If an argument is promotable,
// add it to ArgsToPromote.
SmallPtrSet<Argument*, 8> ArgsToPromote;
SmallPtrSet<Argument*, 8> ByValArgsToTransform;
for (unsigned i = 0; i != PointerArgs.size(); ++i) {
bool isByVal = F->paramHasAttr(PointerArgs[i].second, ParamAttr::ByVal);
if (isSafeToPromoteArgument(PointerArgs[i].first, isByVal))
ArgsToPromote.insert(PointerArgs[i].first);
bool isByVal = F->paramHasAttr(PointerArgs[i].second+1, ParamAttr::ByVal);
// If this is a byval argument, and if the aggregate type is small, just
// pass the elements, which is always safe.
Argument *PtrArg = PointerArgs[i].first;
if (isByVal) {
const Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType();
if (const StructType *STy = dyn_cast<StructType>(AgTy))
if (STy->getNumElements() <= 3) {
// If all the elements are first class types, we can promote it.
bool AllSimple = true;
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
if (!STy->getElementType(i)->isFirstClassType()) {
AllSimple = false;
break;
}
// Safe to transform, don't even bother trying to "promote" it.
// Passing the elements as a scalar will allow scalarrepl to hack on
// the new alloca we introduce.
if (AllSimple) {
ByValArgsToTransform.insert(PtrArg);
continue;
}
}
}
// Otherwise, see if we can promote the pointer to its value.
if (isSafeToPromoteArgument(PtrArg, isByVal))
ArgsToPromote.insert(PtrArg);
}
// No promotable pointer arguments.
if (ArgsToPromote.empty()) return false;
if (ArgsToPromote.empty() && ByValArgsToTransform.empty()) return false;
Function *NewF = DoPromotion(F, ArgsToPromote);
Function *NewF = DoPromotion(F, ArgsToPromote, ByValArgsToTransform);
// Update the call graph to know that the function has been transformed.
getAnalysis<CallGraph>().changeFunction(F, NewF);
@ -344,7 +374,8 @@ namespace {
/// arguments, and returns the new function. At this point, we know that it's
/// safe to do so.
Function *ArgPromotion::DoPromotion(Function *F,
SmallPtrSet<Argument*, 8> &ArgsToPromote) {
SmallPtrSet<Argument*, 8> &ArgsToPromote,
SmallPtrSet<Argument*, 8> &ByValArgsToTransform) {
// Start by computing a new prototype for the function, which is the same as
// the old function, but has modified arguments.
@ -375,15 +406,18 @@ Function *ArgPromotion::DoPromotion(Function *F,
unsigned index = 1;
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
++I, ++index)
if (!ArgsToPromote.count(I)) {
++I, ++index) {
if (ByValArgsToTransform.count(I)) {
// Just add all the struct element types.
const Type *AgTy = cast<PointerType>(I->getType())->getElementType();
const StructType *STy = cast<StructType>(AgTy);
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
Params.push_back(STy->getElementType(i));
++NumByValArgsPromoted;
} else if (!ArgsToPromote.count(I)) {
Params.push_back(I->getType());
if (PAL) {
unsigned attrs = PAL->getParamAttrs(index);
if (attrs)
ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(),
attrs));
}
if (unsigned attrs = PAL ? PAL->getParamAttrs(index) : 0)
ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), attrs));
} else if (I->use_empty()) {
++NumArgumentsDead;
} else {
@ -416,6 +450,7 @@ Function *ArgPromotion::DoPromotion(Function *F,
else
++NumAggregatesPromoted;
}
}
const Type *RetTy = FTy->getReturnType();
@ -462,9 +497,22 @@ Function *ArgPromotion::DoPromotion(Function *F,
CallSite::arg_iterator AI = CS.arg_begin();
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
I != E; ++I, ++AI)
if (!ArgsToPromote.count(I))
if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) {
Args.push_back(*AI); // Unmodified argument
else if (!I->use_empty()) {
} else if (ByValArgsToTransform.count(I)) {
// Emit a GEP and load for each element of the struct.
const Type *AgTy = cast<PointerType>(I->getType())->getElementType();
const StructType *STy = cast<StructType>(AgTy);
Value *Idxs[2] = { ConstantInt::get(Type::Int32Ty, 0), 0 };
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
Idxs[1] = ConstantInt::get(Type::Int32Ty, i);
Value *Idx = new GetElementPtrInst(*AI, Idxs, Idxs+2,
(*AI)->getName()+"."+utostr(i),
Call);
// TODO: Tell AA about the new values?
Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call));
}
} else if (!I->use_empty()) {
// Non-dead argument: insert GEPs and loads as appropriate.
ScalarizeTable &ArgIndices = ScalarizedElements[I];
for (ScalarizeTable::iterator SI = ArgIndices.begin(),
@ -526,17 +574,49 @@ Function *ArgPromotion::DoPromotion(Function *F,
// the new arguments, also transfering over the names as well.
//
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
I2 = NF->arg_begin(); I != E; ++I)
if (!ArgsToPromote.count(I)) {
I2 = NF->arg_begin(); I != E; ++I) {
if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) {
// If this is an unmodified argument, move the name and users over to the
// new version.
I->replaceAllUsesWith(I2);
I2->takeName(I);
AA.replaceWithNewValue(I, I2);
++I2;
} else if (I->use_empty()) {
continue;
}
if (ByValArgsToTransform.count(I)) {
// In the callee, we create an alloca, and store each of the new incoming
// arguments into the alloca.
Instruction *InsertPt = NF->begin()->begin();
// Just add all the struct element types.
const Type *AgTy = cast<PointerType>(I->getType())->getElementType();
Value *TheAlloca = new AllocaInst(AgTy, 0, "", InsertPt);
const StructType *STy = cast<StructType>(AgTy);
Value *Idxs[2] = { ConstantInt::get(Type::Int32Ty, 0), 0 };
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
Idxs[1] = ConstantInt::get(Type::Int32Ty, i);
Value *Idx = new GetElementPtrInst(TheAlloca, Idxs, Idxs+2,
TheAlloca->getName()+"."+utostr(i),
InsertPt);
I2->setName(I->getName()+"."+utostr(i));
new StoreInst(I2++, Idx, InsertPt);
}
// Anything that used the arg should now use the alloca.
I->replaceAllUsesWith(TheAlloca);
TheAlloca->takeName(I);
AA.replaceWithNewValue(I, TheAlloca);
continue;
}
if (I->use_empty()) {
AA.deleteValue(I);
} else {
continue;
}
// Otherwise, if we promoted this argument, then all users are load
// instructions, and all loads should be using the new argument that we
// added.

24
test/Transforms/ArgumentPromotion/byval.ll Normal file
View File

@ -0,0 +1,24 @@
; RUN: llvm-as < %s | opt -argpromotion -scalarrepl | llvm-dis | not grep load
; Argpromote + scalarrepl should change this to passing the two integers by value.
%struct.ss = type { i32, i64 }
define internal void @f(%struct.ss* byval %b) nounwind {
entry:
%tmp = getelementptr %struct.ss* %b, i32 0, i32 0 ; <i32*> [#uses=2]
%tmp1 = load i32* %tmp, align 4 ; <i32> [#uses=1]
%tmp2 = add i32 %tmp1, 1 ; <i32> [#uses=1]
store i32 %tmp2, i32* %tmp, align 4
ret void
}
define i32 @main() nounwind {
entry:
%S = alloca %struct.ss ; <%struct.ss*> [#uses=4]
%tmp1 = getelementptr %struct.ss* %S, i32 0, i32 0 ; <i32*> [#uses=1]
store i32 1, i32* %tmp1, align 8
%tmp4 = getelementptr %struct.ss* %S, i32 0, i32 1 ; <i64*> [#uses=1]
store i64 2, i64* %tmp4, align 4
call void @f( %struct.ss* byval %S ) nounwind
ret i32 0
}