[InstCombine] Don't eagerly propagate nsw for A*B+A*C => A*(B+C)

InstCombine transforms A *nsw B +nsw A *nsw C to A *nsw (B + C).
This is incorrect -- e.g. if A = -1, B = 1, C = INT_SMAX. Then
nothing in the LHS overflows, but the multiplication in RHS overflows.

We need to first make sure that we won't multiple by INT_SMAX + 1.

Test case `add_of_mul` contributed by Sanjoy Das.

This fixes PR23635.

Differential Revision: http://reviews.llvm.org/D9629

llvm-svn: 238066

1 files changed, 42 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/add2.ll b/llvm/test/Transforms/InstCombine/add2.ll
index fbbba5954b3..1af2b0ffbf0 100644
--- a/llvm/test/Transforms/InstCombine/add2.ll
+++ b/llvm/test/Transforms/InstCombine/add2.ll
@@ -273,6 +273,35 @@ define i32 @mul_add_to_mul_6(i32 %x, i32 %y) {
 ; CHECK-NEXT: ret i32 %add
 }
 
+define i16 @mul_add_to_mul_7(i16 %x) {
+  %mul1 = mul nsw i16 %x, 32767
+  %add2 = add nsw i16 %x, %mul1
+  ret i16 %add2
+; CHECK-LABEL: @mul_add_to_mul_7(
+; CHECK-NEXT: %add2 = shl i16 %x, 15
+; CHECK-NEXT: ret i16 %add2
+}
+
+define i16 @mul_add_to_mul_8(i16 %a) {
+  %mul1 = mul nsw i16 %a, 16383
+  %mul2 = mul nsw i16 %a, 16384
+  %add = add nsw i16 %mul1, %mul2
+  ret i16 %add
+; CHECK-LABEL: @mul_add_to_mul_8(
+; CHECK-NEXT: %add = mul nsw i16 %a, 32767
+; CHECK-NEXT: ret i16 %add
+}
+
+define i16 @mul_add_to_mul_9(i16 %a) {
+  %mul1 = mul nsw i16 %a, 16384
+  %mul2 = mul nsw i16 %a, 16384
+  %add = add nsw i16 %mul1, %mul2
+  ret i16 %add
+; CHECK-LABEL: @mul_add_to_mul_9(
+; CHECK-NEXT: %add = shl i16 %a, 15
+; CHECK-NEXT: ret i16 %add
+}
+
 ; This test and the next test verify that when a range metadata is attached to
 ; llvm.cttz, ValueTracking correctly intersects the range specified by the
 ; metadata and the range implied by the intrinsic.
@@ -353,3 +382,16 @@ define i32 @add_nuw_nsw_or_and(i32 %x, i32 %y) {
 ; CHECK-NEXT: add nuw nsw i32 %x, %y
 ; CHECK-NEXT: ret i32
 }
+
+; A *nsw B + A *nsw C != A *nsw (B + C)
+; e.g. A = -1, B = 1, C = INT_SMAX
+
+define i8 @add_of_mul(i8 %x, i8 %y, i8 %z) {
+; CHECK-LABEL: @add_of_mul(
+ entry:
+  %mA = mul nsw i8 %x, %y
+  %mB = mul nsw i8 %x, %z
+; CHECK: %sum = mul i8
+  %sum = add nsw i8 %mA, %mB
+  ret i8 %sum
+}