[llvm] r179786 - In the function InstCombiner::visitExtractElementInst() removed the limitation that extract is promoted over a cast only if the cast has only one use.

[Shemer, Anat]

Thanks for your note. I'm looking at this issue right away.

Regards, Anat

From: Dmitry Babokin [mailto:babokin at gmail.com]
Sent: Monday, April 22, 2013 17:21
To: Shemer, Anat
Cc: llvm-commits
Subject: Re: [llvm] r179786 - In the function InstCombiner::visitExtractElementInst() removed the limitation that extract is promoted over a cast only if the cast has only one use.

This commit introduces a regression. Please see bug http://llvm.org/bugs/show_bug.cgi?id=15818 for more details.

The illegal transformation is the following:
Before:
  %retval.i.i = bitcast <8 x float> %floatval.i.i to <8 x i32>
  %vf.i = bitcast <8 x i32> %retval.i.i to <8 x float>
  %aFOO_load20_offset_load_to_int32 = fptosi <8 x float> %vf.i to <8 x i32>
  %b_load28_to_int32 = fptosi float %b to i32
  %sub_b_load28_to_int32_ = add i32 %b_load28_to_int32, -2
  %v.i.i = extractelement <8 x i32> %aFOO_load20_offset_load_to_int32, i32 %sub_b_load28_to_int32_
After:
  %0 = extractelement <8 x float> %floatval.i.i, i32 %sub_b_load28_to_int32_
  %b_load28_to_int32 = fptosi float %b to i32
  %sub_b_load28_to_int32_ = add i32 %b_load28_to_int32, -2
  %v.i.i = fptosi float %0 to i32

Note that %sub_b_load28_to_int32_ use move before definition.

-Dmitry


On Thu, Apr 18, 2013 at 9:56 PM, Anat Shemer <anat.shemer at intel.com<mailto:anat.shemer at intel.com>> wrote:
Author: ashemer
Date: Thu Apr 18 14:56:44 2013
New Revision: 179786

URL: http://llvm.org/viewvc/llvm-project?rev=179786&view=rev
Log:
In the function InstCombiner::visitExtractElementInst() removed the limitation that extract is promoted over a cast only if the cast has only one use.


Added:
    llvm/trunk/test/Transforms/InstCombine/vec_extract_2elts.ll
Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp?rev=179786&r1=179785&r2=179786&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp Thu Apr 18 14:56:44 2013
@@ -278,10 +278,10 @@ Instruction *InstCombiner::visitExtractE
     } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
       // Canonicalize extractelement(cast) -> cast(extractelement)
       // bitcasts can change the number of vector elements and they cost nothing
-      if (CI->hasOneUse() && EI.hasOneUse() &&
-          (CI->getOpcode() != Instruction::BitCast)) {
-        Value *EE = Builder->CreateExtractElement(CI->getOperand(0),
-                                                  EI.getIndexOperand());
+      if (CI->hasOneUse() && (CI->getOpcode() != Instruction::BitCast)) {
+        Value *EE = InsertNewInstWith(
+                 ExtractElementInst::Create(CI->getOperand(0), EI.getIndexOperand()),
+          *CI);
         return CastInst::Create(CI->getOpcode(), EE, EI.getType());
       }
     }

Added: llvm/trunk/test/Transforms/InstCombine/vec_extract_2elts.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/vec_extract_2elts.ll?rev=179786&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/vec_extract_2elts.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/vec_extract_2elts.ll Thu Apr 18 14:56:44 2013
@@ -0,0 +1,12 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+define void @test(<4 x i32> %v, i64 *%r1, i64 *%r2) {
+;CHECK: %1 = extractelement <4 x i32> %v, i32 0
+;CHECK: %2 = zext i32 %1 to i64
+        %1 = zext <4 x i32> %v to <4 x i64>
+        %2 = extractelement <4 x i64> %1, i32 0
+        store i64 %2, i64 *%r1
+        store i64 %2, i64 *%r2
+        ret void
+}
+


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