Support pointer comparisons against constants, when looking at the inline-cost

savings from a pointer argument becoming an alloca. Sometimes callees will even
compare a pointer to null and then branch to an otherwise unreachable block!
Detect these cases and compute the number of saved instructions, instead of
bailing out and reporting no savings.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148941 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/Inline/alloca-bonus.ll

@@ -42,3 +42,42 @@ define void @inner2(i32 *%ptr) {
   call void @llvm.lifetime.start(i64 0, i8* %E)
   ret void
 }
+
+define void @outer3() {
+; CHECK: @outer3
+; CHECK-NOT: call void @inner3
+  %ptr = alloca i32
+  call void @inner3(i32* %ptr, i1 undef)
+  ret void
+}
+
+define void @inner3(i32 *%ptr, i1 %x) {
+  %A = icmp eq i32* %ptr, null
+  %B = and i1 %x, %A
+  br i1 %A, label %bb.true, label %bb.false
+bb.true:
+  ; This block musn't be counted in the inline cost.
+  %t1 = load i32* %ptr
+  %t2 = add i32 %t1, 1
+  %t3 = add i32 %t2, 1
+  %t4 = add i32 %t3, 1
+  %t5 = add i32 %t4, 1
+  %t6 = add i32 %t5, 1
+  %t7 = add i32 %t6, 1
+  %t8 = add i32 %t7, 1
+  %t9 = add i32 %t8, 1
+  %t10 = add i32 %t9, 1
+  %t11 = add i32 %t10, 1
+  %t12 = add i32 %t11, 1
+  %t13 = add i32 %t12, 1
+  %t14 = add i32 %t13, 1
+  %t15 = add i32 %t14, 1
+  %t16 = add i32 %t15, 1
+  %t17 = add i32 %t16, 1
+  %t18 = add i32 %t17, 1
+  %t19 = add i32 %t18, 1
+  %t20 = add i32 %t19, 1
+  ret void
+bb.false:
+  ret void
+}