[llvm] [ARM] support -mlong-calls -fPIC on arm32 #39970 (PR #147313)

[Eli Friedman via llvm-commits]

================
@@ -46,4 +49,62 @@ entry:
 
 declare void @callee0()
 
+; PIC-O0-LONGCALL-LABEL: global_func:
+; PIC-O0-LONGCALL:       bx lr
+
+; PIC-LONGCALL-LABEL: global_func:
+; PIC-LONGCALL:       bx lr
+define void @global_func() {
+entry:
+  ret void
+}
+
+; PIC-O0-LONGCALL-LABEL: test_global:
+; PIC-O0-LONGCALL:       push {r11, lr}
+; PIC-O0-LONGCALL:       ldr r0, [[GOT_LABEL:.*]]
+; PIC-O0-LONGCALL:       ldr r0, [pc, r0]
+; PIC-O0-LONGCALL:       blx r0
+; PIC-O0-LONGCALL:       pop {r11, pc}
+; PIC-O0-LONGCALL:       [[GOT_LABEL]]:
+; PIC-O0-LONGCALL:       .long global_func(GOT_PREL)
+
+; PIC-LONGCALL-LABEL: test_global:
+; PIC-LONGCALL:       push {r11, lr}
+; PIC-LONGCALL:       ldr r0, [[GOT_LABEL:.*]]
+; PIC-LONGCALL:       ldr r0, [pc, r0]
+; PIC-LONGCALL:       blx r0
+; PIC-LONGCALL:       pop {r11, pc}
+; PIC-LONGCALL:       [[GOT_LABEL]]:
+; PIC-LONGCALL:       .long global_func(GOT_PREL)
+define void @test_global() {
+entry:
+  call void @global_func()
+  ret void
+}
+
+; PIC-O0-LONGCALL-LABEL: test_memset:
+; PIC-O0-LONGCALL:       push {r11, lr}
+; PIC-O0-LONGCALL:       ldr r3, [[GOT_LABEL:.*]]
+; PIC-O0-LONGCALL:       ldr r3, [pc, r3]
+; PIC-O0-LONGCALL:       blx r3
+; PIC-O0-LONGCALL:       pop {r11, pc}
+; PIC-O0-LONGCALL:       [[GOT_LABEL]]:
+; PIC-O0-LONGCALL:       .long memset(GOT_PREL)
+
+; PIC-LONGCALL-LABEL: test_memset:
+; PIC-LONGCALL:       push {r11, lr}
+; PIC-LONGCALL:       ldr r3, [[MEMSET_LABEL:.*]]
+; PIC-LONGCALL:       add r3, pc, r3
----------------
efriedma-quic wrote:

The -O1 code is wrong.  The -O0 code is also wrong.

Look at what we do for something like `extern int x; int* f() { return &x; }`.  Or look at what we do for `__attribute((visibility("hidden"))) extern int x; int* f() { return &x; }`.

https://github.com/llvm/llvm-project/pull/147313