InstSimplify: If divisor element is undef simplify to undef

Summary:
If any vector divisor element is undef, we can arbitrarily choose it be
zero which would make the div/rem an undef value by definition.

Reviewers: spatel, reames

Reviewed By: spatel

Subscribers: magabari, llvm-commits

Differential Revision: https://reviews.llvm.org/D42485

llvm-svn: 323343

2 files changed, 32 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstSimplify/div.ll b/llvm/test/Transforms/InstSimplify/div.ll
index a1cc8572724..1eb767e17bf 100644
--- a/llvm/test/Transforms/InstSimplify/div.ll
+++ b/llvm/test/Transforms/InstSimplify/div.ll
@@ -34,6 +34,22 @@ define <2 x i8> @udiv_zero_elt_vec(<2 x i8> %x) {
   ret <2 x i8> %div
 }
 
+define <2 x i8> @sdiv_undef_elt_vec(<2 x i8> %x) {
+; CHECK-LABEL: @sdiv_undef_elt_vec(
+; CHECK-NEXT:    ret <2 x i8> undef
+;
+  %div = sdiv <2 x i8> %x, <i8 -42, i8 undef>
+  ret <2 x i8> %div
+}
+
+define <2 x i8> @udiv_undef_elt_vec(<2 x i8> %x) {
+; CHECK-LABEL: @udiv_undef_elt_vec(
+; CHECK-NEXT:    ret <2 x i8> undef
+;
+  %div = udiv <2 x i8> %x, <i8 undef, i8 42>
+  ret <2 x i8> %div
+}
+
 ; Division-by-zero is undef. UB in any vector lane means the whole op is undef.
 ; Thus, we can simplify this: if any element of 'y' is 0, we can do anything.
 ; Therefore, assume that all elements of 'y' must be 1.
diff --git a/llvm/test/Transforms/InstSimplify/rem.ll b/llvm/test/Transforms/InstSimplify/rem.ll
index a015d4c43e0..e1fc6684cf9 100644
--- a/llvm/test/Transforms/InstSimplify/rem.ll
+++ b/llvm/test/Transforms/InstSimplify/rem.ll
@@ -35,6 +35,22 @@ define <2 x i8> @urem_zero_elt_vec(<2 x i8> %x) {
   ret <2 x i8> %rem
 }
 
+define <2 x i8> @srem_undef_elt_vec(<2 x i8> %x) {
+; CHECK-LABEL: @srem_undef_elt_vec(
+; CHECK-NEXT:    ret <2 x i8> undef
+;
+  %rem = srem <2 x i8> %x, <i8 -42, i8 undef>
+  ret <2 x i8> %rem
+}
+
+define <2 x i8> @urem_undef_elt_vec(<2 x i8> %x) {
+; CHECK-LABEL: @urem_undef_elt_vec(
+; CHECK-NEXT:    ret <2 x i8> undef
+;
+  %rem = urem <2 x i8> %x, <i8 undef, i8 42>
+  ret <2 x i8> %rem
+}
+
 ; Division-by-zero is undef. UB in any vector lane means the whole op is undef.
 ; Thus, we can simplify this: if any element of 'y' is 0, we can do anything.
 ; Therefore, assume that all elements of 'y' must be 1.