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Ignore loads from and stores to local memory (i.e. allocas)
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
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@ -86,17 +86,34 @@ bool AddReadAttrs::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
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// Scan the function body for instructions that may read or write memory.
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// Scan the function body for instructions that may read or write memory.
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for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
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for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
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CallSite CS = CallSite::get(&*II);
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Instruction *I = &*II;
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// Ignore calls to functions in the same SCC.
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// Some instructions can be ignored even if they read or write memory.
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if (CS.getInstruction() && SCCNodes.count(CG[CS.getCalledFunction()]))
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// Detect these now, skipping to the next instruction if one is found.
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continue;
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CallSite CS = CallSite::get(I);
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if (CS.getInstruction()) {
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// Ignore calls to functions in the same SCC.
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if (SCCNodes.count(CG[CS.getCalledFunction()]))
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continue;
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} else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
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Value *Target = LI->getPointerOperand()->getUnderlyingObject();
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// Ignore loads from local memory.
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if (isa<AllocaInst>(Target))
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continue;
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} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
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Value *Target = SI->getPointerOperand()->getUnderlyingObject();
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// Ignore stores to local memory.
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if (isa<AllocaInst>(Target))
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continue;
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}
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if (II->mayWriteToMemory())
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// Any remaining instructions need to be taken seriously! Check if they
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// read or write memory.
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if (I->mayWriteToMemory())
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// Writes memory. Just give up.
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// Writes memory. Just give up.
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return false;
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return false;
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// If this instruction may read memory, remember that.
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ReadsMemory |= II->mayReadFromMemory();
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ReadsMemory |= I->mayReadFromMemory();
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}
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}
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}
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}
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10
test/Transforms/AddReadAttrs/2008-10-04-LocalMemory.ll
Normal file
10
test/Transforms/AddReadAttrs/2008-10-04-LocalMemory.ll
Normal file
@ -0,0 +1,10 @@
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; RUN: llvm-as < %s | opt -addreadattrs | llvm-dis | grep readnone | count 2
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declare i32 @g(i32*) readnone
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define i32 @f() {
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%x = alloca i32 ; <i32*> [#uses=2]
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store i32 0, i32* %x
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%y = call i32 @g(i32* %x) ; <i32> [#uses=1]
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ret i32 %y
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}
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