Teach basicaa that memset's modref set is at worst "mod" and never
contains "ref".
Enhance DSE to use a modref query instead of a store-specific hack
to generalize the "ignore may-alias stores" optimization to handle
memset and memcpy.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120368 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index bf1b689..3e63424 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -703,6 +703,8 @@
if (isNoAlias(Location(Dest, Len), Loc))
return NoModRef;
}
+ // We know that memset doesn't load anything.
+ Min = Mod;
break;
case Intrinsic::atomic_cmp_swap:
case Intrinsic::atomic_swap:
diff --git a/lib/Transforms/Scalar/DeadStoreElimination.cpp b/lib/Transforms/Scalar/DeadStoreElimination.cpp
index dd66416..d9f5bc5 100644
--- a/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -191,6 +191,7 @@
I1Size >= I2Size;
}
+
bool DSE::runOnBasicBlock(BasicBlock &BB) {
MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
TD = getAnalysisIfAvailable<TargetData>();
@@ -239,7 +240,7 @@
}
}
}
-
+
if (!InstDep.isDef()) {
// If this is a may-aliased store that is clobbering the store value, we
// can keep searching past it for another must-aliased pointer that stores
@@ -250,12 +251,16 @@
// we can remove the first store to P even though we don't know if P and Q
// alias.
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
- AliasAnalysis::Location Loc =
- getAnalysis<AliasAnalysis>().getLocation(SI);
- while (InstDep.isClobber() && isa<StoreInst>(InstDep.getInst()) &&
- InstDep.getInst() != &BB.front())
- InstDep = MD.getPointerDependencyFrom(Loc, false, InstDep.getInst(),
- &BB);
+ AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
+ AliasAnalysis::Location Loc = AA.getLocation(SI);
+ while (InstDep.isClobber() && InstDep.getInst() != &BB.front()) {
+ // Can't look past this instruction if it might read 'Loc'.
+ if (AA.getModRefInfo(InstDep.getInst(), Loc) & AliasAnalysis::Ref)
+ break;
+
+ InstDep = MD.getPointerDependencyFrom(Loc, false,
+ InstDep.getInst(), &BB);
+ }
}
}
diff --git a/test/Transforms/DeadStoreElimination/simple.ll b/test/Transforms/DeadStoreElimination/simple.ll
index 05e0d35..c426c0a 100644
--- a/test/Transforms/DeadStoreElimination/simple.ll
+++ b/test/Transforms/DeadStoreElimination/simple.ll
@@ -54,3 +54,17 @@
; CHECK-NEXT: volatile load
; CHECK-NEXT: ret void
}
+
+declare void @llvm.memset.i32(i8*, i8, i32, i32)
+
+; Should delete store of 10 even though memset is a may-store to P (P and Q may
+; alias).
+define void @test6(i32 *%p, i8 *%q) {
+ store i32 10, i32* %p, align 4 ;; dead.
+ call void @llvm.memset.i32(i8* %q, i8 42, i32 900, i32 1)
+ store i32 30, i32* %p, align 4
+ ret void
+; CHECK: @test6
+; CHECK-NEXT: call void @llvm.memset
+}
+