[llvm-commits] [llvm] r144730 - /llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp

[Chad Rosier]

Author: mcrosier
Date: Tue Nov 15 17:34:05 2011
New Revision: 144730

URL: http://llvm.org/viewvc/llvm-project?rev=144730&view=rev
Log:
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

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp?rev=144730&r1=144729&r2=144730&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp Tue Nov 15 17:34:05 2011
@@ -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() &&