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Partially address a README by having functionattrs consider calls to

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memcpy, memset and other intrinsics that only access their arguments
to be readnone if the intrinsic's arguments all point to local memory.
This improves the testcase in the README to readonly, but it could in
theory be made readnone, however this would involve more sophisticated
analysis that looks through the memcpy.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92829 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2010-01-06 08:45:52 +00:00
parent eaba5102e4
commit 7c422ac216
6 changed files with 60 additions and 9 deletions
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4
include/llvm/Analysis/AliasAnalysis.h
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@ -197,6 +197,10 @@ public:
virtual ModRefBehavior getModRefBehavior(Function *F,
std::vector<PointerAccessInfo> *Info = 0);
/// getModRefBehavior - Return the modref behavior of the intrinsic with the
/// given id.
static ModRefBehavior getModRefBehavior(unsigned iid);
/// doesNotAccessMemory - If the specified call is known to never read or
/// write memory, return true. If the call only reads from known-constant
/// memory, it is also legal to return true. Calls that unwind the stack

11
lib/Analysis/AliasAnalysis.cpp
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@ -116,13 +116,16 @@ AliasAnalysis::getModRefBehavior(Function *F,
return DoesNotAccessMemory;
if (F->onlyReadsMemory())
return OnlyReadsMemory;
if (unsigned id = F->getIntrinsicID()) {
if (unsigned id = F->getIntrinsicID())
return getModRefBehavior(id);
}
return UnknownModRefBehavior;
}
AliasAnalysis::ModRefBehavior AliasAnalysis::getModRefBehavior(unsigned iid) {
#define GET_INTRINSIC_MODREF_BEHAVIOR
#include "llvm/Intrinsics.gen"
#undef GET_INTRINSIC_MODREF_BEHAVIOR
}
}
return UnknownModRefBehavior;
}
AliasAnalysis::ModRefResult

4
lib/Target/README.txt
View File

@ -1678,8 +1678,8 @@ And functionattrs doesn't realize that the p.0 load points to function local
memory.
Also, functionattrs doesn't know about memcpy/memset. This function should be
marked readnone, since it only twiddles local memory, but functionattrs doesn't
handle memset/memcpy/memmove aggressively:
marked readnone rather than readonly, since it only twiddles local memory, but
functionattrs doesn't handle memset/memcpy/memmove aggressively:
struct X { int *p; int *q; };
int foo() {

15
lib/Transforms/IPO/FunctionAttrs.cpp
View File

@ -136,6 +136,21 @@ bool FunctionAttrs::AddReadAttrs(const std::vector<CallGraphNode *> &SCC) {
// Ignore calls to functions in the same SCC.
if (SCCNodes.count(CS.getCalledFunction()))
continue;
// Ignore intrinsics that only access local memory.
if (unsigned id = CS.getCalledFunction()->getIntrinsicID())
if (AliasAnalysis::getModRefBehavior(id) ==
AliasAnalysis::AccessesArguments) {
// Check that all pointer arguments point to local memory.
for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
CI != CE; ++CI) {
Value *Arg = *CI;
if (isa<PointerType>(Arg->getType()) && !PointsToLocalMemory(Arg))
// Writes memory. Just give up.
return false;
}
// Only reads and writes local memory.
continue;
}
} else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
// Ignore loads from local memory.
if (PointsToLocalMemory(LI->getPointerOperand()))

33
test/Transforms/FunctionAttrs/2008-10-04-LocalMemory.ll
View File

@ -1,6 +1,8 @@
; RUN: opt < %s -functionattrs -S | grep readnone | count 2
; RUN: opt < %s -functionattrs -S | grep readonly | count 3
declare i32 @g(i32*) readnone
%struct.X = type { i32*, i32* }
declare i32 @g(i32*) readonly
define i32 @f() {
%x = alloca i32 ; <i32*> [#uses=2]
@ -8,3 +10,30 @@ define i32 @f() {
%y = call i32 @g(i32* %x) ; <i32> [#uses=1]
ret i32 %y
}
define i32 @foo() nounwind {
entry:
%y = alloca %struct.X ; <%struct.X*> [#uses=2]
%x = alloca %struct.X ; <%struct.X*> [#uses=2]
%j = alloca i32 ; <i32*> [#uses=2]
%i = alloca i32 ; <i32*> [#uses=2]
%"alloca point" = bitcast i32 0 to i32 ; <i32> [#uses=0]
store i32 0, i32* %i, align 4
store i32 1, i32* %j, align 4
%0 = getelementptr inbounds %struct.X* %y, i32 0, i32 0 ; <i32**> [#uses=1]
store i32* %i, i32** %0, align 8
%1 = getelementptr inbounds %struct.X* %x, i32 0, i32 1 ; <i32**> [#uses=1]
store i32* %j, i32** %1, align 8
%x1 = bitcast %struct.X* %x to i8* ; <i8*> [#uses=2]
%y2 = bitcast %struct.X* %y to i8* ; <i8*> [#uses=1]
call void @llvm.memcpy.i64(i8* %x1, i8* %y2, i64 8, i32 1)
%2 = bitcast i8* %x1 to i32** ; <i32**> [#uses=1]
%3 = load i32** %2, align 8 ; <i32*> [#uses=1]
%4 = load i32* %3, align 4 ; <i32> [#uses=1]
br label %return
return: ; preds = %entry
ret i32 %4
}
declare void @llvm.memcpy.i64(i8* nocapture, i8* nocapture, i64, i32) nounwind

2
utils/TableGen/IntrinsicEmitter.cpp
View File

@ -522,7 +522,7 @@ void IntrinsicEmitter::
EmitModRefBehavior(const std::vector<CodeGenIntrinsic> &Ints, raw_ostream &OS){
OS << "// Determine intrinsic alias analysis mod/ref behavior.\n";
OS << "#ifdef GET_INTRINSIC_MODREF_BEHAVIOR\n";
OS << "switch (id) {\n";
OS << "switch (iid) {\n";
OS << "default:\n return UnknownModRefBehavior;\n";
for (unsigned i = 0, e = Ints.size(); i != e; ++i) {
if (Ints[i].ModRef == CodeGenIntrinsic::WriteMem)