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
diff --git a/lib/Transforms/IPO/AddReadAttrs.cpp b/lib/Transforms/IPO/AddReadAttrs.cpp
index 7af071c..5460a5b 100644
--- a/lib/Transforms/IPO/AddReadAttrs.cpp
+++ b/lib/Transforms/IPO/AddReadAttrs.cpp
@@ -86,17 +86,34 @@
// 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();
}
}