[ARM] [Windows] Use IMAGE_SYM_CLASS_STATIC for private functions (#101828)

For functions with private linkage, pick
IMAGE_SYM_CLASS_STATIC rather than IMAGE_SYM_CLASS_EXTERNAL;
GlobalValue::isInternalLinkage() only checks for
InternalLinkage, while GlobalValue::isLocalLinkage() checks for both
InternalLinkage and PrivateLinkage.

This matches what the AArch64 target does, since commit
3406934.

This activates a preexisting fix for the AArch64 target from
1e7f592, for the ARM target as well.

When a relocation points at a symbol, one usually can convey an offset
to the symbol by encoding it as an immediate in the instruction.
However, for the ARM and AArch64 branch instructions, the immediate
stored in the instruction is ignored by MS link.exe (and lld-link
matches this aspect). (It would be simple to extend lld-link to support
it - but such object files would be incompatible with MS link.exe.)

This was worked around by 1e7f592 by
emitting symbols into the object file symbol table, for temporary
symbols that otherwise would have been omitted, if they have the class
IMAGE_SYM_CLASS_STATIC, in order to avoid needing an offset in the
relocated instruction.

This change gives the symbols generated from functions with the IR level
"private" linkage the right class, to activate that workaround.

This fixes #100101, fixing
code generation for coroutines for Windows on ARM. After the change in
f786881, coroutines generate a function
with private linkage, and calls to this function were previously broken
for this target.

Author: mstorsjo

llvm/lib/Target/ARM/ARMAsmPrinter.cpp

@@ -153,9 +153,9 @@ bool ARMAsmPrinter::runOnMachineFunction(MachineFunction &MF) {
     OptimizationGoals = 0;
 
   if (Subtarget->isTargetCOFF()) {
-    bool Internal = F.hasInternalLinkage();
-    COFF::SymbolStorageClass Scl = Internal ? COFF::IMAGE_SYM_CLASS_STATIC
-                                            : COFF::IMAGE_SYM_CLASS_EXTERNAL;
+    bool Local = F.hasLocalLinkage();
+    COFF::SymbolStorageClass Scl =
+        Local ? COFF::IMAGE_SYM_CLASS_STATIC : COFF::IMAGE_SYM_CLASS_EXTERNAL;
     int Type = COFF::IMAGE_SYM_DTYPE_FUNCTION << COFF::SCT_COMPLEX_TYPE_SHIFT;
 
     OutStreamer->beginCOFFSymbolDef(CurrentFnSym);

llvm/test/CodeGen/ARM/Windows/private-func.ll

@@ -0,0 +1,17 @@
+; RUN: llc -mtriple thumbv7-windows -filetype asm -o - %s | FileCheck %s
+
+define dso_local void @func1() {
+entry:
+  call void @func2()
+  ret void
+}
+
+define private void @func2() {
+entry:
+  ret void
+}
+
+; CHECK:      .def    .Lfunc2;
+; CHECK-NEXT: .scl    3;
+; CHECK-NEXT: .type   32;
+; CHECK-NEXT: .endef

llvm/test/MC/ARM/Windows/branch-reloc-offset.s

@@ -0,0 +1,57 @@
+// RUN: llvm-mc -triple thumbv7-windows-gnu -filetype obj %s -o - | llvm-objdump -D -r - | FileCheck %s
+
+    .text
+main:
+    nop
+    b .Ltarget
+    b .Lother_target
+
+// A private label target in the same section
+    .def .Ltarget
+    .scl 3
+    .type 32
+    .endef
+    .p2align 2
+.Ltarget:
+    bx lr
+
+// A private label target in another section
+    .section "other", "xr"
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    nop
+    .def .Lother_target
+    .scl 3
+    .type 32
+    .endef
+    .p2align 2
+.Lother_target:
+    bx lr
+
+// Check that both branches have a relocation with a zero offset.
+//
+// CHECK: 00000000 <main>:
+// CHECK:        0: bf00          nop
+// CHECK:        2: f000 b800     b.w     0x6 <main+0x6>          @ imm = #0x0
+// CHECK:                         00000002:  IMAGE_REL_ARM_BRANCH24T      .Ltarget
+// CHECK:        6: f000 b800     b.w     0xa <main+0xa>          @ imm = #0x0
+// CHECK:                         00000006:  IMAGE_REL_ARM_BRANCH24T      .Lother_target
+// CHECK:        a: bf00          nop
+// CHECK: 0000000c <.Ltarget>:
+// CHECK:        c: 4770          bx      lr
+// CHECK: 00000000 <other>:
+// CHECK:        0: bf00          nop
+// CHECK:        2: bf00          nop
+// CHECK:        4: bf00          nop
+// CHECK:        6: bf00          nop
+// CHECK:        8: bf00          nop
+// CHECK:        a: bf00          nop
+// CHECK:        c: bf00          nop
+// CHECK:        e: bf00          nop
+// CHECK: 00000010 <.Lother_target>:
+// CHECK:       10: 4770          bx      lr