FastIsel: take care to update iterators when removing instructions.

We keep a few iterators into the basic block we're selecting while
performing FastISel. Usually this is fine, but occasionally code wants
to remove already-emitted instructions. When this happens we have to be
careful to update those iterators so they're not pointint at dangling
memory.

llvm-svn: 349365

1 files changed, 25 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/AArch64/fast-isel-erase.ll b/llvm/test/CodeGen/AArch64/fast-isel-erase.ll
new file mode 100644
index 00000000000..e8265bce9fe
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/fast-isel-erase.ll
@@ -0,0 +1,25 @@
+; RUN: llc -mtriple=arm64-apple-ios -o - %s -fast-isel=1 -O0 | FileCheck %s
+
+; The zext can be folded into the load and removed, but doing so can invalidate
+; pointers internal to FastISel and cause a crash so it must be done carefully.
+define i32 @test() {
+; CHECK-LABEL: test:
+; CHECK: ldrh
+; CHECK: bl _callee
+; CHECK-NOT: uxth
+
+entry:
+  store i32 undef, i32* undef, align 4
+  %t81 = load i16, i16* undef, align 2
+  call void @callee()
+  %t82 = zext i16 %t81 to i32
+  %t83 = shl i32 %t82, 16
+  %t84 = or i32 undef, %t83
+  br label %end
+
+end:
+  %val = phi i32 [%t84, %entry]
+  ret i32 %val
+}
+
+declare void @callee()