Pre-commit test showing bug #80287

This test shows the bug where LR is used as a general-purpose register
on a code path where it is not spilled to the stack.

(cherry picked from commit 8779cf6)

llvm/test/CodeGen/ARM/ldst-opt-lr-restored.ll

@@ -0,0 +1,55 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc -mtriple thumbv7a-none-eabi < %s | FileCheck %s
+
+@val0 = global i32 0, align 4
+@val1 = global i32 0, align 4
+@val2 = global i32 0, align 4
+
+define i32 @foo(ptr %ctx) {
+; CHECK-LABEL: foo:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    cbz r0, .LBB0_2
+; CHECK-NEXT:  @ %bb.1: @ %if.end
+; CHECK-NEXT:    movw r2, :lower16:val0
+; CHECK-NEXT:    mov r1, r0
+; CHECK-NEXT:    movs r0, #0
+; CHECK-NEXT:    movw r12, :lower16:val2
+; CHECK-NEXT:    movw r3, :lower16:val1
+; CHECK-NEXT:    movt r2, :upper16:val0
+; CHECK-NEXT:    add.w lr, r1, #4
+; CHECK-NEXT:    movt r12, :upper16:val2
+; CHECK-NEXT:    movt r3, :upper16:val1
+; CHECK-NEXT:    stm.w lr, {r2, r3, r12}
+; CHECK-NEXT:    str r0, [r1, #16]
+; CHECK-NEXT:    bx lr
+; CHECK-NEXT:  .LBB0_2: @ %if.then
+; CHECK-NEXT:    .save {r7, lr}
+; CHECK-NEXT:    push {r7, lr}
+; CHECK-NEXT:    bl bar
+; CHECK-NEXT:    mov.w r0, #-1
+; CHECK-NEXT:    pop {r7, pc}
+entry:
+  %tobool.not = icmp eq ptr %ctx, null
+  br i1 %tobool.not, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  tail call void @bar() #2
+  br label %return
+
+if.end:                                           ; preds = %entry
+  %cmd_a = getelementptr inbounds i8, ptr %ctx, i32 4
+  store ptr @val0, ptr %cmd_a, align 4
+  %cmd_b = getelementptr inbounds i8, ptr %ctx, i32 8
+  store ptr @val1, ptr %cmd_b, align 4
+  %cmd_c = getelementptr inbounds i8, ptr %ctx, i32 12
+  store ptr @val2, ptr %cmd_c, align 4
+  %cmd_d = getelementptr inbounds i8, ptr %ctx, i32 16
+  store ptr null, ptr %cmd_d, align 4
+  br label %return
+
+return:                                           ; preds = %if.end, %if.then
+  %retval.0 = phi i32 [ 0, %if.end ], [ -1, %if.then ]
+  ret i32 %retval.0
+}
+
+declare void @bar()