[llvm-commits] [PATCH] Instcombine : extractelement(cast) -> cast(extractelement)

[Rotem, Nadav]

Hi,

Please review this patch to the InstCombine pass. In this patch I optimize extractelements which uses the value of cast instructions. I attempt to switch the order of the extract and the cast. I noticed a major performance boost on my workloads.

Nadav

Index: ../llvm/test/Transforms/InstCombine/ExtractCast.ll
===================================================================
--- ../llvm/test/Transforms/InstCombine/ExtractCast.ll  (revision 0)
+++ ../llvm/test/Transforms/InstCombine/ExtractCast.ll  (revision 0)
@@ -0,0 +1,27 @@
+; RUN: opt < %s -instcombine -S -o - | FileCheck %s
+
+; CHECK: @a
+define i32 @a(<4 x i64> %I) {
+entry:
+; CHECK-NOT: trunc <4 x i64>
+        %J = trunc <4 x i64> %I to <4 x i32>
+        %K = extractelement <4 x i32> %J, i32 3
+; CHECK: extractelement <4 x i64>
+; CHECK: trunc i64
+; CHECK: ret
+        ret i32 %K
+}
+
+
+; CHECK: @b
+define i32 @b(<4 x float> %I) {
+entry:
+; CHECK-NOT: fptosi <4 x float>
+        %J = fptosi <4 x float> %I to <4 x i32>
+        %K = extractelement <4 x i32> %J, i32 3
+; CHECK: extractelement <4 x float>
+; CHECK: fptosi float
+; CHECK: ret
+        ret i32 %K
+}
+

Index: ../llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
===================================================================
--- ../llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp (revision 128529)
+++ ../llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp (working copy)
@@ -230,8 +230,17 @@
                                           ConstantInt::get(Int32Ty,
                                                            SrcIdx, false));
       }
+    } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
+      // Canonicalize extractelement(cast) -> cast(extractelement)
+      // Ignore bitcasts, because they change the number of vector elements
+      if (CI->hasOneUse() && EI.hasOneUse() &&
+          (CI->getOpcode() != Instruction::BitCast)) {
+        Value *EE = Builder->CreateExtractElement(CI->getOperand(0),
+                                                  EI.getIndexOperand());
+        return CastInst::Create(CI->getOpcode(), cast<Instruction>(EE),
+                                EI.getType());
+      }
     }
-    // FIXME: Canonicalize extractelement(bitcast) -> bitcast(extractelement)
   }
   return 0;
}
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