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Ignore loads from and stores to local memory (i.e. allocas)

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when deciding whether to mark a function readnone/readonly.
Since the pass is currently run before SROA, this may be
quite helpful.  Requested by Chris on IRC.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57050 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2008-10-04 13:24:24 +00:00
parent 26e4b216c0
commit c82b6a1ed2
2 changed files with 34 additions and 7 deletions
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31
lib/Transforms/IPO/AddReadAttrs.cpp
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@ -86,17 +86,34 @@ bool AddReadAttrs::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
// Scan the function body for instructions that may read or write memory.
for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
CallSite CS = CallSite::get(&*II);
Instruction *I = &*II;
// Ignore calls to functions in the same SCC.
if (CS.getInstruction() && SCCNodes.count(CG[CS.getCalledFunction()]))
continue;
// Some instructions can be ignored even if they read or write memory.
// Detect these now, skipping to the next instruction if one is found.
CallSite CS = CallSite::get(I);
if (CS.getInstruction()) {
// Ignore calls to functions in the same 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))
continue;
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
Value *Target = SI->getPointerOperand()->getUnderlyingObject();
// Ignore stores to local memory.
if (isa<AllocaInst>(Target))
continue;
}
if (II->mayWriteToMemory())
// Any remaining instructions need to be taken seriously! Check if they
// read or write memory.
if (I->mayWriteToMemory())
// Writes memory. Just give up.
return false;
ReadsMemory |= II->mayReadFromMemory();
// If this instruction may read memory, remember that.
ReadsMemory |= I->mayReadFromMemory();
}
}

10
test/Transforms/AddReadAttrs/2008-10-04-LocalMemory.ll Normal file
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@ -0,0 +1,10 @@
; RUN: llvm-as < %s | opt -addreadattrs | llvm-dis | grep readnone | count 2
declare i32 @g(i32*) readnone
define i32 @f() {
%x = alloca i32 ; <i32*> [#uses=2]
store i32 0, i32* %x
%y = call i32 @g(i32* %x) ; <i32> [#uses=1]
ret i32 %y
}