DAGCombiner: Assume invariant load cannot alias a store

The motivation is to allow GatherAllAliases / FindBetterChain
to not give up on dependent loads of a pointer from constant memory.

This is important for AMDGPU, because most loads are pointers
derived from a load of a kernel argument from constant memory.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241948 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Matt Arsenault
2015-07-10 22:17:40 +00:00
parent d819fac294
commit ee6d5d1c9e
2 changed files with 44 additions and 0 deletions

View File

@@ -13844,6 +13844,15 @@ bool DAGCombiner::isAlias(LSBaseSDNode *Op0, LSBaseSDNode *Op1) const {
// If they are both volatile then they cannot be reordered.
if (Op0->isVolatile() && Op1->isVolatile()) return true;
// If one operation reads from invariant memory, and the other may store, they
// cannot alias. These should really be checking the equivalent of mayWrite,
// but it only matters for memory nodes other than load /store.
if (Op0->isInvariant() && Op1->writeMem())
return false;
if (Op1->isInvariant() && Op0->writeMem())
return false;
// Gather base node and offset information.
SDValue Base1, Base2;
int64_t Offset1, Offset2;