InstCombine, InstSimplify: (%X /s C1) /s C2 isn't always 0 when C1 * C2 overflow

consider:
C1 = INT_MIN
C2 = -1

C1 * C2 overflows without a doubt but consider the following:
%x = i32 INT_MIN

This means that (%X /s C1) is 1 and (%X /s C1) /s C2 is -1.

N. B.  Move the unsigned version of this transform to InstSimplify, it
doesn't create any new instructions.

This fixes PR21243.

llvm-svn: 219567

2 files changed, 16 insertions, 14 deletions

diff --git a/llvm/test/Transforms/InstCombine/2008-02-16-SDivOverflow.ll b/llvm/test/Transforms/InstCombine/2008-02-16-SDivOverflow.ll
deleted file mode 100644
index 917d3d9436b..00000000000
--- a/llvm/test/Transforms/InstCombine/2008-02-16-SDivOverflow.ll
+++ /dev/null
@@ -1,14 +0,0 @@
-; RUN: opt < %s -instcombine -S | grep "ret i.* 0" | count 2
-; PR2048
-
-define i32 @i(i32 %a) {
-  %tmp1 = sdiv i32 %a, -1431655765
-  %tmp2 = sdiv i32 %tmp1, 3
-  ret i32 %tmp2
-}
-
-define i8 @j(i8 %a) {
-  %tmp1 = sdiv i8 %a, 64
-  %tmp2 = sdiv i8 %tmp1, 3
-  ret i8 %tmp2
-}
diff --git a/llvm/test/Transforms/InstSimplify/exact-nsw-nuw.ll b/llvm/test/Transforms/InstSimplify/exact-nsw-nuw.ll
index a0e326b13c0..5ccc8083e64 100644
--- a/llvm/test/Transforms/InstSimplify/exact-nsw-nuw.ll
+++ b/llvm/test/Transforms/InstSimplify/exact-nsw-nuw.ll
@@ -42,3 +42,19 @@ define i32 @shift5(i32 %A, i32 %B) {
   %D = ashr i32 %C, %B
   ret i32 %D
 }
+
+; CHECK-LABEL: @div1(
+; CHECK: ret i32 0
+define i32 @div1(i32 %V) {
+  %A = udiv i32 %V, -2147483648
+  %B = udiv i32 %A, -2147483648
+  ret i32 %B
+}
+
+; CHECK-LABEL: @div2(
+; CHECK-NOT: ret i32 0
+define i32 @div2(i32 %V) {
+  %A = sdiv i32 %V, -1
+  %B = sdiv i32 %A, -2147483648
+  ret i32 %B
+}