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Add trivial support for the invariance intrinsics to memdep. This logic is

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purely local for now.

llvm-svn: 85378
This commit is contained in:
Owen Anderson 2009-10-28 06:18:42 +00:00
parent 1efa0c450a
commit 6cf32f04df
2 changed files with 56 additions and 1 deletions
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36
lib/Analysis/MemoryDependenceAnalysis.cpp
View File

@ -171,13 +171,42 @@ getCallSiteDependencyFrom(CallSite CS, bool isReadOnlyCall,
/// location depends. If isLoad is true, this routine ignore may-aliases with
/// read-only operations.
MemDepResult MemoryDependenceAnalysis::
getPointerDependencyFrom(Value *MemPtr, uint64_t MemSize, bool isLoad,
getPointerDependencyFrom(Value *MemPtr, uint64_t MemSize, bool isLoad,
BasicBlock::iterator ScanIt, BasicBlock *BB) {
Value* invariantTag = 0;
// Walk backwards through the basic block, looking for dependencies.
while (ScanIt != BB->begin()) {
Instruction *Inst = --ScanIt;
// If we're in an invariant region, no dependencies can be found before
// we pass an invariant-begin marker.
if (invariantTag == Inst) {
invariantTag = 0;
continue;
// If we pass an invariant-end marker, then we've just entered an invariant
// region and can start ignoring dependencies.
} else if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) {
if (II->getIntrinsicID() == Intrinsic::invariant_end) {
uint64_t invariantSize = ~0ULL;
if (ConstantInt* CI = dyn_cast<ConstantInt>(II->getOperand(2)))
invariantSize = CI->getZExtValue();
AliasAnalysis::AliasResult R =
AA->alias(II->getOperand(3), invariantSize, MemPtr, MemSize);
if (R == AliasAnalysis::MustAlias) {
invariantTag = II->getOperand(1);
continue;
}
}
}
// If we're querying on a load and we're in an invariant region, we're done
// at this point. Nothing a load depends on can live in an invariant region.
if (isLoad && invariantTag) continue;
// Debug intrinsics don't cause dependences.
if (isa<DbgInfoIntrinsic>(Inst)) continue;
@ -201,6 +230,11 @@ getPointerDependencyFrom(Value *MemPtr, uint64_t MemSize, bool isLoad,
return MemDepResult::getDef(Inst);
}
// If we're querying on a store and we're in an invariant region, we're done
// at this point. The only things that stores depend on that could exist in
// an invariant region are loads, which we've already checked.
if (invariantTag) continue;
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
// If alias analysis can tell that this store is guaranteed to not modify
// the query pointer, ignore it. Use getModRefInfo to handle cases where

21
test/Transforms/GVN/invariant-simple.ll Normal file
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@ -0,0 +1,21 @@
; RUN: opt < %s -gvn -S | FileCheck %s
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target triple = "i386-apple-darwin7"
define i8 @test(i8* %P) nounwind {
; CHECK: @test
; CHECK-NOT: load
; CHECK: ret i8
entry:
store i8 1, i8* %P
%0 = call {}* @llvm.invariant.start(i64 32, i8* %P)
%1 = tail call i32 @foo(i8* %P)
call void @llvm.invariant.end({}* %0, i64 32, i8* %P)
%2 = load i8* %P
ret i8 %2
}
declare i32 @foo(i8*) nounwind
declare {}* @llvm.invariant.start(i64 %S, i8* nocapture %P) readonly
declare void @llvm.invariant.end({}* %S, i64 %SS, i8* nocapture %P)