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 e8f8c73d6883c8046f83ad5c2cd16d757a6d9aa8..c58d730454f00c1c365e72949ce16a8762322ce9 100644 (file)
--- a/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -96,6 +96,11 @@ bool FastISel::hasTrivialKill(const Value *V) const {
         !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() &&