GEPs with all zero indices are trivially coalesced by fast-isel. For example,
%arrayidx135 = getelementptr inbounds [4 x [4 x [4 x [4 x i32]]]]* %M0, i32 0, i64 0
%arrayidx136 = getelementptr inbounds [4 x [4 x [4 x i32]]]* %arrayidx135, i32 0, i64 %idxprom134
Prior to this commit, the GEP instruction that defines %arrayidx136 thought that
%arrayidx135 was a trivial kill. The GEP that defines %arrayidx135 doesn't
generate any code and thus %M0 gets folded into the second GEP. Thus, we need
to look through GEPs with all zero indices.
rdar://10443319
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@144730 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/FastISel.cpp b/lib/CodeGen/SelectionDAG/FastISel.cpp
index e8f8c73..c58d730 100644
--- a/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -96,6 +96,11 @@
!hasTrivialKill(Cast->getOperand(0)))
return false;
+ // GEPs with all zero indices are trivially coalesced by fast-isel.
+ if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I))
+ if (GEP->hasAllZeroIndices() && !hasTrivialKill(GEP->getOperand(0)))
+ return false;
+
// Only instructions with a single use in the same basic block are considered
// to have trivial kills.
return I->hasOneUse() &&