[llvm] r297409 - [ConstantFold] vector div/rem with any zero element in divisor is undef

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Thu Mar  9 14:42:30 2017
New Revision: 297409

URL: http://llvm.org/viewvc/llvm-project?rev=297409&view=rev
Log:
[ConstantFold] vector div/rem with any zero element in divisor is undef

Follow-up for:
https://reviews.llvm.org/D30665
https://reviews.llvm.org/rL297390

Modified:
    llvm/trunk/lib/IR/ConstantFold.cpp
    llvm/trunk/test/Transforms/InstSimplify/div.ll
    llvm/trunk/test/Transforms/InstSimplify/rem.ll

Modified: llvm/trunk/lib/IR/ConstantFold.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/ConstantFold.cpp?rev=297409&r1=297408&r2=297409&view=diff
==============================================================================
--- llvm/trunk/lib/IR/ConstantFold.cpp (original)
+++ llvm/trunk/lib/IR/ConstantFold.cpp Thu Mar  9 14:42:30 2017
@@ -1209,10 +1209,15 @@ Constant *llvm::ConstantFoldBinaryInstru
     SmallVector<Constant*, 16> Result;
     Type *Ty = IntegerType::get(VTy->getContext(), 32);
     for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) {
-      Constant *LHS =
-        ConstantExpr::getExtractElement(C1, ConstantInt::get(Ty, i));
-      Constant *RHS =
-        ConstantExpr::getExtractElement(C2, ConstantInt::get(Ty, i));
+      Constant *ExtractIdx = ConstantInt::get(Ty, i);
+      Constant *LHS = ConstantExpr::getExtractElement(C1, ExtractIdx);
+      Constant *RHS = ConstantExpr::getExtractElement(C2, ExtractIdx);
+
+      // If any element of a divisor vector is zero, the whole op is undef.
+      if ((Opcode == Instruction::SDiv || Opcode == Instruction::UDiv ||
+           Opcode == Instruction::SRem || Opcode == Instruction::URem) &&
+          RHS->isNullValue())
+        return UndefValue::get(VTy);
 
       Result.push_back(ConstantExpr::get(Opcode, LHS, RHS));
     }

Modified: llvm/trunk/test/Transforms/InstSimplify/div.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/div.ll?rev=297409&r1=297408&r2=297409&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/div.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/div.ll Thu Mar  9 14:42:30 2017
@@ -4,7 +4,7 @@
 
 define <2 x i8> @sdiv_zero_elt_vec_constfold(<2 x i8> %x) {
 ; CHECK-LABEL: @sdiv_zero_elt_vec_constfold(
-; CHECK-NEXT:    ret <2 x i8> <i8 undef, i8 0>
+; CHECK-NEXT:    ret <2 x i8> undef
 ;
   %div = sdiv <2 x i8> <i8 1, i8 2>, <i8 0, i8 -42>
   ret <2 x i8> %div
@@ -12,7 +12,7 @@ define <2 x i8> @sdiv_zero_elt_vec_const
 
 define <2 x i8> @udiv_zero_elt_vec_constfold(<2 x i8> %x) {
 ; CHECK-LABEL: @udiv_zero_elt_vec_constfold(
-; CHECK-NEXT:    ret <2 x i8> <i8 0, i8 undef>
+; CHECK-NEXT:    ret <2 x i8> undef
 ;
   %div = udiv <2 x i8> <i8 1, i8 2>, <i8 42, i8 0>
   ret <2 x i8> %div

Modified: llvm/trunk/test/Transforms/InstSimplify/rem.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/rem.ll?rev=297409&r1=297408&r2=297409&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/rem.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/rem.ll Thu Mar  9 14:42:30 2017
@@ -5,7 +5,7 @@
 
 define <2 x i8> @srem_zero_elt_vec_constfold(<2 x i8> %x) {
 ; CHECK-LABEL: @srem_zero_elt_vec_constfold(
-; CHECK-NEXT:    ret <2 x i8> <i8 undef, i8 2>
+; CHECK-NEXT:    ret <2 x i8> undef
 ;
   %rem = srem <2 x i8> <i8 1, i8 2>, <i8 0, i8 -42>
   ret <2 x i8> %rem
@@ -13,7 +13,7 @@ define <2 x i8> @srem_zero_elt_vec_const
 
 define <2 x i8> @urem_zero_elt_vec_constfold(<2 x i8> %x) {
 ; CHECK-LABEL: @urem_zero_elt_vec_constfold(
-; CHECK-NEXT:    ret <2 x i8> <i8 1, i8 undef>
+; CHECK-NEXT:    ret <2 x i8> undef
 ;
   %rem = urem <2 x i8> <i8 1, i8 2>, <i8 42, i8 0>
   ret <2 x i8> %rem