Hi Tobias.
I worked on enabling Polly accepting non affine memory accesses and I
produced a patch.
Great.
I saw that there were a lot of updates in Polly recently, so I had to
redo a lot of the work I did and that slowed me quite a bit.
Ups, sorry! However, I believe without these changes detecting non-affine memory access functions would have been a lot more complicated.
I tested the patch on some programs and it seems to work and not to
break anything, but you know the topic much better than me, so if you
find something wrong please tell me! (at least it shouldn't produce a
crash I believe ... I tested the patch quite a lot from that point of
view ...). The patch is in the attachment to this mail and was last
tested on LLVM SVN revision 144502 .
OK. Review is inlined in the patch.
I also found a bug in polly or ISL/GMP libraries. If polly encounters
an array access of type:
A[i][i]
it enters an infinite loop (I believe it is an infinite loop because I
waited 5 minutes and it didn't terminate compiling a code that was
like 15 lines long). I tried to track down the problem with gdb , but
it seems to be in some gmp function called by ISL of which I'm not a
very expert of.
[remove backtrace & code]
I actually don't know if it is an ISL bug or an improper use by polly.
To compile isl I use gmp-5.0.2
I will look into this.
--- ./include/polly/ScopDetection.h 2011-11-13 02:37:59.000000000 +0100
+++ ../llvm2/tools/polly/./include/polly/ScopDetection.h 2011-11-13 01:11:17.000000000 +0100
@@ -145,6 +145,8 @@
/// @return True if the call instruction is valid, false otherwise.
static bool isValidCallInst(CallInst&CI);
+ const Value *GetBaseValue(const SCEV *S) const;
Why is this function needed? For me it looks like it implements
the same as
SCEVValue *Operand = dyn_cast<SCEVValue>(getPointerOperand())
if (!Operand)
return invalid Value;
return Operand->getValue();
/// @brief Check if a memory access can be part of a Scop.
///
/// @param Inst The instruction accessing the memory.
--- ./include/polly/TempScopInfo.h 2011-11-13 02:37:59.000000000 +0100
+++ ../llvm2/tools/polly/./include/polly/TempScopInfo.h 2011-11-13 02:34:47.000000000 +0100
@@ -45,12 +45,13 @@
private:
unsigned ElemBytes;
TypeKind Type;
+ bool is_affine;
I think IsAffine matches more the LLVM coding conventions.
public:
explicit IRAccess (TypeKind Type, const Value *BaseAddress,
- const SCEV *Offset, unsigned elemBytes)
+ const SCEV *Offset, unsigned elemBytes, bool affine)
'affine' should start with an uppercase letter. Polly itself has some inconsistent naming, but we started to follow the LLVM coding conventions since a while.
: BaseAddress(BaseAddress), Offset(Offset),
- ElemBytes(elemBytes), Type(Type) {}
+ ElemBytes(elemBytes), Type(Type), is_affine(affine) {}
enum TypeKind getType() const { return Type; }
@@ -60,7 +61,10 @@
unsigned getElemSizeInBytes() const { return ElemBytes; }
+ bool isAffine() const { return is_affine; }
+
bool isRead() const { return Type == READ; }
+
};
class Comparison {
--- ./lib/Analysis/ScopDetection.cpp 2011-11-13 02:38:06.000000000 +0100
+++ ../llvm2/tools/polly/./lib/Analysis/ScopDetection.cpp 2011-11-13 01:28:00.000000000 +0100
@@ -226,6 +226,24 @@
return false;
}
+const Value *ScopDetection::GetBaseValue(const SCEV *S) const {
+ if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
+ // In an addrec, assume that the base will be in the start, rather
+ // than the step.
+ return GetBaseValue(AR->getStart());
+ } else if (const SCEVAddExpr *A = dyn_cast<SCEVAddExpr>(S)) {
+ // If there's a pointer operand, it'll be sorted at the end of the list.
+ const SCEV *Last = A->getOperand(A->getNumOperands()-1);
+ if (Last->getType()->isPointerTy())
+ return GetBaseValue(Last);
+ } else if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
+ // This is a leaf node.
+ return U->getValue();
+ }
+ // No Identified object found.
+ return 0;
+}
As remarked earlier, I believ this can be replaced by getPointerOperand().
bool ScopDetection::isValidMemoryAccess(Instruction&Inst,
DetectionContext&Context) const {
Value *Ptr = getPointerOperand(Inst);
@@ -236,8 +254,12 @@
BasePointer = dyn_cast<SCEVUnknown>(SE->getPointerBase(AccessFunction));
if (!BasePointer)
- INVALID(AffFunc, "No base pointer");
-
+ {
+// INVALID(AffFunc, "No base pointer");
+ BaseValue = (Value*) GetBaseValue(AccessFunction);
+ }
+ else
+ {
BaseValue = BasePointer->getValue();
I don't see a need for any change here. Both functions get the base pointer and we should fail, if we cannot derive a base pointer. Do you have a test case where getPointerBase() does not yield a valid base pointer, but GetBaseValue(AccessFunction) does?
if (isa<UndefValue>(BaseValue))
@@ -245,8 +267,9 @@
AccessFunction = SE->getMinusSCEV(AccessFunction, BasePointer);
- if (!isAffineExpr(&Context.CurRegion, AccessFunction, *SE, BaseValue))
- INVALID(AffFunc, "Bad memory address "<< *AccessFunction);
+ //if (!isAffineExpr(&Context.CurRegion, AccessFunction, *SE, BaseValue))
+ // INVALID(AffFunc, "Bad memory address "<< *AccessFunction);
Can you leave this and add a command line option
'-polly-allow-nonaffine' to allow non affine access functions.
+ }
// FIXME: Alias Analysis thinks IntToPtrInst aliases with alloca instructions
// created by IndependentBlocks Pass.
--- ./lib/Analysis/ScopInfo.cpp 2011-11-13 02:38:06.000000000 +0100
+++ ../llvm2/tools/polly/./lib/Analysis/ScopInfo.cpp 2011-11-13 02:36:12.000000000 +0100
@@ -310,9 +310,13 @@
Type = Access.isRead() ? Read : Write;
statement = Statement;
- isl_pw_aff *Affine = SCEVAffinator::getPwAff(Statement, Access.getOffset());
BaseAddr = Access.getBase();
+ if (Access.isAffine())
+ {
This should be
if (Access.isAffine()) {
+
+ isl_pw_aff *Affine = SCEVAffinator::getPwAff(Statement, Access.getOffset());
+
setBaseName();
// Devide the access function by the size of the elements in the array.
@@ -334,6 +338,12 @@
AccessRelation = isl_map_set_tuple_name(AccessRelation, isl_dim_out,
getBaseName().c_str());
}
+ else
+ {
this should be
} else {
+ Type = MayWrite;
You are right, we should use may-accesses here. But why always setting the type to may-write? A read should remain a read (as there is no difference between read and may-read).
+ AccessRelation = isl_map_from_basic_map(createBasicAccessMap(Statement));
+ }
+}
void MemoryAccess::realignParams() {
isl_space *ParamSpace = statement->getParent()->getParamSpace();
--- ./lib/Analysis/TempScopInfo.cpp 2011-11-13 02:38:06.000000000 +0100
+++ ../llvm2/tools/polly/./lib/Analysis/TempScopInfo.cpp 2011-11-13 02:35:22.000000000 +0100
@@ -98,13 +98,24 @@
dyn_cast<SCEVUnknown>(SE->getPointerBase(AccessFunction));
assert(BasePointer&& "Could not find base pointer");
-
AccessFunction = SE->getMinusSCEV(AccessFunction, BasePointer);
+
+ if (isAffineExpr(&R, AccessFunction, *SE, BasePointer->getValue()))
+ {
Put the '{' in the previous line.
+
Functions.push_back(std::make_pair(IRAccess(Type,
BasePointer->getValue(),
- AccessFunction, Size),
+ AccessFunction, Size, true),
&Inst));
}
+ else
+ {
This should be
} else {
+ Functions.push_back(std::make_pair(IRAccess(Type,
+ BasePointer->getValue(),
+ AccessFunction, Size, false),
+&Inst));
+ }
+ }
}
if (Functions.empty())
Besides the comments above, the patch looks great. It is a nice improvement to Polly. Can you repost it after the comments are addressed? Also could you include a minimal test case in the patch, that verifies this features is working correctly.
Thanks
Tobi
P.S.: Please post patches to the mailing lists.
