[llvm-dev] [PATCH] patch for missed constantFold optimization in InstCombine

[Budukh, Tejas via llvm-dev]

Hi,
Any reviewers for this patch ? Any suggestions ?
Opt tool's output for this ll before and after the patch is also attached.

Thanks,
Tejas

From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Budukh, Tejas via llvm-dev
Sent: Friday, November 06, 2015 9:43 AM
To: llvm-dev at lists.llvm.org
Subject: [llvm-dev] [PATCH] patch for missed constantFold optimization in InstCombine

Hi All,
llvm::ConstantFoldCompareInstOperands misses an optimization when it tries to constantFold a compare instruction containing addrspacecast instead of combination of ptrtoint and inttoptr. Adding the patched code snippet in the code would enable the pass to handle addrspacecast and constantFold the missing cases.
Attached is the .ll file for the reproducer. Let me know if there are any suggestions/comments or I can commit the patch.

Patched code :
Index: ConstantFolding.cpp
===================================================================
diff --git a/llvm/trunk/lib/Analysis/ConstantFolding.cpp b/llvm/trunk/lib/Analysis/ConstantFolding.cpp
--- a/llvm/trunk/lib/Analysis/ConstantFolding.cpp            (revision 252222)
+++ b/llvm/trunk/lib/Analysis/ConstantFolding.cpp        (working copy)
@@ -1137,6 +1137,12 @@
           return ConstantFoldCompareInstOperands(Predicate, C, Null, DL, TLI);
         }
       }
+
+      if (CE0->getOpcode() == Instruction::AddrSpaceCast) {
+          Constant *C = CE0->getOperand(0);
+          Constant *Null = Constant::getNullValue(C->getType());
+          return ConstantFoldCompareInstOperands(Predicate, C, Null, TD, TLI);
+      }
     }

     if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(Ops1)) {


Thanks,
Tejas
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