[ARM] Pass thumb as architecture to the underlying tools, when targeting windows

[mstorsjo]

Summary

This makes sure that the thumb section flag gets set by the assembler.

This is an alternative fix to D22776.

[rengolin]

LGTM. I'll add the test to LLVM as a separate commit.

lib/Driver/ToolChain.cpp

499

This makes sense to me.

test/Driver/thumb-attributes.s

1

But we don't usually do asm tests in Clang. I can add this test to LLVM's MC dir.

[mstorsjo]

test/Driver/thumb-attributes.s

1

Do tests there also use the clang frontend driver? If you change it to test with llvm-mc with a thumb triplet, you won't actually test anything of this.

(Also, as long as this test uses clang, should it perhaps need a "// REQUIRES: arm-registered-target" at the start? I had that included in the other clang test, which was based on other old tests, while this one was changed from llvm-mc to clang.)

[rengolin]

test/Driver/thumb-attributes.s

1

If you change it to test with llvm-mc with a thumb triplet, you won't actually test anything of this.

That's a good point, actually. A better test for this one thing would be to make sure that whatever C file would generate an IR with a triple that is actually "thumb".

[mstorsjo]

Updated the test to only check what triplet is passed to the assembler

[rengolin]

Committed as r276869.

lib/Driver/ToolChain.cpp

if (getTriple().isOSWindows())
       ThumbDefault = true;
     std::string ArchName;
     if (IsBigEndian)
       ArchName = "armeb";
     else
       ArchName = "arm";
 
     // Assembly files should start in ARM mode, unless arch is M-profile.
+    // Windows is always thumb.
     if ((InputType != types::TY_PP_Asm && Args.hasFlag(options::OPT_mthumb,
-         options::OPT_mno_thumb, ThumbDefault)) || IsMProfile) {
+         options::OPT_mno_thumb, ThumbDefault)) || IsMProfile ||
+         getTriple().isOSWindows()) {
       if (IsBigEndian)
         ArchName = "thumbeb";
       else
         ArchName = "thumb";
     }
     Triple.setArchName(ArchName + Suffix.str());
 
     return Triple.getTriple();

test/Driver/thumb-attributes.s

+@ RUN: %clang -target armv7-windows-itanium -c -o - %s \
+@ RUN:   | llvm-readobj -s - | FileCheck %s
+
+  .syntax unified
+  .thumb
+
+  .text
+
+  .global function
+  .thumb_func
+function:
+  bx lr
+
+@ CHECK: Sections [
+@ CHECK:   Section {
+@ CHECK:     Name: .text
+@ CHECK:     Characteristics [
+@ CHECK-DAG:   IMAGE_SCN_CNT_CODE
+@ CHECK-DAG:   IMAGE_SCN_MEM_16BIT
+@ CHECK:     ]
+@ CHECK:   }
+@ CHECK: ]