From 5cf1d925cccec8815bf85c3870c087df508513eb Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Thu, 9 Mar 2017 20:42:30 +0000
Subject: [PATCH] [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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297409 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/IR/ConstantFold.cpp             | 13 +++++++++----
 test/Transforms/InstSimplify/div.ll |  4 ++--
 test/Transforms/InstSimplify/rem.ll |  4 ++--
 3 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/lib/IR/ConstantFold.cpp b/lib/IR/ConstantFold.cpp
index 13241c37675..dc7728a4841 100644
--- a/lib/IR/ConstantFold.cpp
+++ b/lib/IR/ConstantFold.cpp
@@ -1209,10 +1209,15 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
     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));
     }
diff --git a/test/Transforms/InstSimplify/div.ll b/test/Transforms/InstSimplify/div.ll
index 6412bdfffe3..560d3eea933 100644
--- a/test/Transforms/InstSimplify/div.ll
+++ b/test/Transforms/InstSimplify/div.ll
@@ -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_constfold(<2 x i8> %x) {
 
 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
diff --git a/test/Transforms/InstSimplify/rem.ll b/test/Transforms/InstSimplify/rem.ll
index 90a0e658235..c60b728cad2 100644
--- a/test/Transforms/InstSimplify/rem.ll
+++ b/test/Transforms/InstSimplify/rem.ll
@@ -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_constfold(<2 x i8> %x) {
 
 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
-- 
2.40.0