[FastISel][AArch64] Don't fold instructions that are not in the same basic block.

This fix checks first if the instruction to be folded (e.g. sign-/zero-extend,
or shift) is in the same machine basic block as the instruction we are folding
into.

Not doing so can result in incorrect code, because the value might not be
live-out of the basic block, where the value is defined.

This fixes rdar://problem/18169495.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216700 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/AArch64/fast-isel-folding.ll

@@ -0,0 +1,54 @@
+; RUN: llc -mtriple=aarch64-apple-darwin -O0 -fast-isel-abort -verify-machineinstrs < %s
+
+; Test that we don't fold the shift.
+define i64 @fold_shift_test(i64 %a, i1 %c) {
+  %1 = sub i64 %a, 8
+  %2 = ashr i64 %1, 3
+  br i1 %c, label %bb1, label %bb2
+bb1:
+  %3 = icmp ult i64 0, %2
+  br i1 %3, label %bb2, label %bb3
+bb2:
+  ret i64 1
+bb3:
+  ret i64 2
+}
+
+; Test that we don't fold the sign-extend.
+define i64 @fold_sext_test1(i32 %a, i1 %c) {
+  %1 = sub i32 %a, 8
+  %2 = sext i32 %1 to i64
+  br i1 %c, label %bb1, label %bb2
+bb1:
+  %3 = icmp ult i64 0, %2
+  br i1 %3, label %bb2, label %bb3
+bb2:
+  ret i64 1
+bb3:
+  ret i64 2
+}
+
+; Test that we don't fold the sign-extend.
+define i64 @fold_sext_test2(i32 %a, i1 %c) {
+  %1 = sub i32 %a, 8
+  %2 = sext i32 %1 to i64
+  br i1 %c, label %bb1, label %bb2
+bb1:
+  %3 = shl i64 %2, 4
+  ret i64 %3
+bb2:
+  ret i64 %2
+}
+
+; Test that we clear the kill flag.
+define i32 @fold_kill_test(i32 %a) {
+  %1 = sub i32 %a, 8
+  %2 = shl i32 %1, 3
+  %3 = icmp ult i32 0, %2
+  br i1 %3, label %bb1, label %bb2
+bb1:
+  ret i32 %2
+bb2:
+  %4 = add i32 %2, 4
+  ret i32 %4
+}