[llvm] r235854 - Constfold insertelement to undef when index is out-of-bounds

[Pawel Bylica]

Author: chfast
Date: Mon Apr 27 04:30:49 2015
New Revision: 235854

URL: http://llvm.org/viewvc/llvm-project?rev=235854&view=rev
Log:
Constfold insertelement to undef when index is out-of-bounds

Summary:
This patch adds constant folding of insertelement instruction to undef value when index operand is constant and is not less than vector size or is undef.

InstCombine does not support this case, but I'm happy to add it there also if this change is accepted.

Test Plan: Unittests and regression tests for ConstProp pass.

Reviewers: majnemer

Reviewed By: majnemer

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9287

Modified:
    llvm/trunk/lib/IR/ConstantFold.cpp
    llvm/trunk/test/Transforms/ConstProp/InsertElement.ll
    llvm/trunk/unittests/IR/ConstantsTest.cpp

Modified: llvm/trunk/lib/IR/ConstantFold.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/ConstantFold.cpp?rev=235854&r1=235853&r2=235854&view=diff
==============================================================================
--- llvm/trunk/lib/IR/ConstantFold.cpp (original)
+++ llvm/trunk/lib/IR/ConstantFold.cpp Mon Apr 27 04:30:49 2015
@@ -800,23 +800,30 @@ Constant *llvm::ConstantFoldExtractEleme
 Constant *llvm::ConstantFoldInsertElementInstruction(Constant *Val,
                                                      Constant *Elt,
                                                      Constant *Idx) {
+  if (isa<UndefValue>(Idx))
+    return UndefValue::get(Val->getType());
+
   ConstantInt *CIdx = dyn_cast<ConstantInt>(Idx);
   if (!CIdx) return nullptr;
-  const APInt &IdxVal = CIdx->getValue();
-  
+
+  unsigned NumElts = Val->getType()->getVectorNumElements();
+  if (CIdx->uge(NumElts))
+    return UndefValue::get(Val->getType());
+
   SmallVector<Constant*, 16> Result;
-  Type *Ty = IntegerType::get(Val->getContext(), 32);
-  for (unsigned i = 0, e = Val->getType()->getVectorNumElements(); i != e; ++i){
+  Result.reserve(NumElts);
+  auto *Ty = Type::getInt32Ty(Val->getContext());
+  uint64_t IdxVal = CIdx->getZExtValue();
+  for (unsigned i = 0; i != NumElts; ++i) {    
     if (i == IdxVal) {
       Result.push_back(Elt);
       continue;
     }
     
-    Constant *C =
-      ConstantExpr::getExtractElement(Val, ConstantInt::get(Ty, i));
+    Constant *C = ConstantExpr::getExtractElement(Val, ConstantInt::get(Ty, i));
     Result.push_back(C);
   }
-  
+
   return ConstantVector::get(Result);
 }
 

Modified: llvm/trunk/test/Transforms/ConstProp/InsertElement.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/ConstProp/InsertElement.ll?rev=235854&r1=235853&r2=235854&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/ConstProp/InsertElement.ll (original)
+++ llvm/trunk/test/Transforms/ConstProp/InsertElement.ll Mon Apr 27 04:30:49 2015
@@ -1,12 +1,32 @@
 ; RUN: opt < %s -constprop -S | FileCheck %s
 
+; CHECK-LABEL: @test1
 define i32 @test1() {
   %A = bitcast i32 2139171423 to float
   %B = insertelement <1 x float> undef, float %A, i32 0
   %C = extractelement <1 x float> %B, i32 0
   %D = bitcast float %C to i32
   ret i32 %D
-; CHECK: @test1
 ; CHECK: ret i32 2139171423
 }
 
+; CHECK-LABEL: @insertelement
+define <4 x i64> @insertelement() {
+  %vec1 = insertelement <4 x i64> undef, i64 -1, i32 0
+  %vec2 = insertelement <4 x i64> %vec1, i64 -2, i32 1
+  %vec3 = insertelement <4 x i64> %vec2, i64 -3, i32 2
+  %vec4 = insertelement <4 x i64> %vec3, i64 -4, i32 3
+  ; CHECK: ret <4 x i64> <i64 -1, i64 -2, i64 -3, i64 -4>
+  ret <4 x i64> %vec4
+}
+
+; CHECK-LABEL: @insertelement_undef
+define <4 x i64> @insertelement_undef() {
+  %vec1 = insertelement <4 x i64> undef, i64 -1, i32 0
+  %vec2 = insertelement <4 x i64> %vec1, i64 -2, i32 1
+  %vec3 = insertelement <4 x i64> %vec2, i64 -3, i32 2
+  %vec4 = insertelement <4 x i64> %vec3, i64 -4, i32 3
+  %vec5 = insertelement <4 x i64> %vec3, i64 -5, i32 4
+  ; CHECK: ret <4 x i64> undef
+  ret <4 x i64> %vec5
+}

Modified: llvm/trunk/unittests/IR/ConstantsTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/IR/ConstantsTest.cpp?rev=235854&r1=235853&r2=235854&view=diff
==============================================================================
--- llvm/trunk/unittests/IR/ConstantsTest.cpp (original)
+++ llvm/trunk/unittests/IR/ConstantsTest.cpp Mon Apr 27 04:30:49 2015
@@ -190,7 +190,10 @@ TEST(ConstantsTest, AsInstructionsTest)
   Constant *Two = ConstantInt::get(Int64Ty, 2);
   Constant *Big = ConstantInt::get(getGlobalContext(),
                                    APInt{256, uint64_t(-1), true});
-  Constant *Undef = UndefValue::get(Int64Ty);
+  Constant *Elt = ConstantInt::get(Int16Ty, 2015);
+  Constant *Undef16  = UndefValue::get(Int16Ty);
+  Constant *Undef64  = UndefValue::get(Int64Ty);
+  Constant *UndefV16 = UndefValue::get(P6->getType());
 
   #define P0STR "ptrtoint (i32** @dummy to i32)"
   #define P1STR "uitofp (i32 ptrtoint (i32** @dummy to i32) to float)"
@@ -260,9 +263,15 @@ TEST(ConstantsTest, AsInstructionsTest)
   CHECK(ConstantExpr::getExtractElement(P6, One), "extractelement <2 x i16> "
         P6STR ", i32 1");
 
-  EXPECT_TRUE(isa<UndefValue>(ConstantExpr::getExtractElement(P6, Two)));
-  EXPECT_TRUE(isa<UndefValue>(ConstantExpr::getExtractElement(P6, Big)));
-  EXPECT_TRUE(isa<UndefValue>(ConstantExpr::getExtractElement(P6, Undef)));
+  EXPECT_EQ(Undef16, ConstantExpr::getExtractElement(P6, Two));
+  EXPECT_EQ(Undef16, ConstantExpr::getExtractElement(P6, Big));
+  EXPECT_EQ(Undef16, ConstantExpr::getExtractElement(P6, Undef64));
+
+  EXPECT_EQ(Elt, ConstantExpr::getExtractElement(
+                 ConstantExpr::getInsertElement(P6, Elt, One), One));
+  EXPECT_EQ(UndefV16, ConstantExpr::getInsertElement(P6, Elt, Two));
+  EXPECT_EQ(UndefV16, ConstantExpr::getInsertElement(P6, Elt, Big));
+  EXPECT_EQ(UndefV16, ConstantExpr::getInsertElement(P6, Elt, Undef64));
 }
 
 #ifdef GTEST_HAS_DEATH_TEST