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Allow readnone functions to read (and write!) global

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constants, since doing so is irrelevant for aliasing
purposes.  While this doesn't increase the total number
of functions marked readonly or readnone in MultiSource/
Applications (3089), it does result in 12 functions being
marked readnone rather than readonly.
Before:
  readnone: 820
  readonly: 2269
After:
  readnone: 832
  readonly: 2257


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61469 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2008-12-29 11:34:09 +00:00
parent 2b7fc1ef53
commit 516ec62bfe
2 changed files with 27 additions and 4 deletions
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23
lib/Transforms/IPO/AddReadAttrs.cpp
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@ -17,6 +17,7 @@
#define DEBUG_TYPE "addreadattrs"
#include "llvm/Transforms/IPO.h"
#include "llvm/CallGraphSCCPass.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/ADT/SmallPtrSet.h"
@ -40,6 +41,8 @@ namespace {
AU.setPreservesCFG();
CallGraphSCCPass::getAnalysisUsage(AU);
}
bool PointsToLocalMemory(Value *V);
};
}
@ -50,6 +53,20 @@ X("addreadattrs", "Mark functions readnone/readonly");
Pass *llvm::createAddReadAttrsPass() { return new AddReadAttrs(); }
/// PointsToLocalMemory - Returns whether the given pointer value points to
/// memory that is local to the function. Global constants are considered
/// local to all functions.
bool AddReadAttrs::PointsToLocalMemory(Value *V) {
V = V->getUnderlyingObject();
// An alloca instruction defines local memory.
if (isa<AllocaInst>(V))
return true;
// A global constant counts as local memory for our purposes.
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
return GV->isConstant();
return false;
}
bool AddReadAttrs::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
SmallPtrSet<CallGraphNode *, 8> SCCNodes;
CallGraph &CG = getAnalysis<CallGraph>();
@ -96,14 +113,12 @@ bool AddReadAttrs::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
if (SCCNodes.count(CG[CS.getCalledFunction()]))
continue;
} else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
Value *Target = LI->getPointerOperand()->getUnderlyingObject();
// Ignore loads from local memory.
if (isa<AllocaInst>(Target))
if (PointsToLocalMemory(LI->getPointerOperand()))
continue;
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
Value *Target = SI->getPointerOperand()->getUnderlyingObject();
// Ignore stores to local memory.
if (isa<AllocaInst>(Target))
if (PointsToLocalMemory(SI->getPointerOperand()))
continue;
}

8
test/Transforms/AddReadAttrs/2008-12-29-Constant.ll Normal file
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@ -0,0 +1,8 @@
; RUN: llvm-as < %s | opt -addreadattrs | llvm-dis | grep readnone
@s = external constant i8 ; <i8*> [#uses=1]
define i8 @f() {
%tmp = load i8* @s ; <i8> [#uses=1]
ret i8 %tmp
}