Emit the ARM build attributes ABI_PCS_wchar_t and ABI_enum_size.

Emit the ARM build attributes ABI_PCS_wchar_t and ABI_enum_size based on
module flags metadata.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211349 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LangRef.rst

@@ -3146,6 +3146,42 @@ Each individual option is required to be either a valid option for the target's
 linker, or an option that is reserved by the target specific assembly writer or
 object file emitter. No other aspect of these options is defined by the IR.
 
+C type width Module Flags Metadata
+----------------------------------
+
+The ARM backend emits a section into each generated object file describing the
+options that it was compiled with (in a compiler-independent way) to prevent
+linking incompatible objects, and to allow automatic library selection. Some
+of these options are not visible at the IR level, namely wchar_t width and enum
+width.
+
+To pass this information to the backend, these options are encoded in module
+flags metadata, using the following key-value pairs:
+
+.. list-table::
+   :header-rows: 1
+   :widths: 30 70
+
+   * - Key
+     - Value
+
+   * - short_wchar
+     - * 0 --- sizeof(wchar_t) == 4
+       * 1 --- sizeof(wchar_t) == 2
+
+   * - short_enum
+     - * 0 --- Enums are at least as large as an ``int``.
+       * 1 --- Enums are stored in the smallest integer type which can
+         represent all of its values.
+
+For example, the following metadata section specifies that the module was
+compiled with a ``wchar_t`` width of 4 bytes, and the underlying type of an
+enum is the smallest type which can represent all of its values::
+
+    !llvm.module.flags = !{!0, !1}
+    !0 = metadata !{i32 1, metadata !"short_wchar", i32 1}
+    !1 = metadata !{i32 1, metadata !"short_enum", i32 0}
+
 .. _intrinsicglobalvariables:
 
 Intrinsic Global Variables

include/llvm/Support/ARMBuildAttributes.h

@@ -159,13 +159,28 @@ enum {
   AddressDirect = 1, // Address imported data directly
   AddressGOT = 2, // Address imported data indirectly (via GOT)
 
+  // Tag_ABI_PCS_wchar_t, (=18), uleb128
+  WCharProhibited = 0,  // wchar_t is not used
+  WCharWidth2Bytes = 2, // sizeof(wchar_t) == 2
+  WCharWidth4Bytes = 4, // sizeof(wchar_t) == 4
+
   // Tag_ABI_FP_denormal, (=20), uleb128
   PreserveFPSign = 2, // sign when flushed-to-zero is preserved
 
   // Tag_ABI_FP_number_model, (=23), uleb128
   AllowRTABI = 2,  // numbers, infinities, and one quiet NaN (see [RTABI])
   AllowIEE754 = 3, // this code to use all the IEEE 754-defined FP encodings
 
+  // Tag_ABI_enum_size, (=26), uleb128
+  EnumProhibited = 0, // The user prohibited the use of enums when building
+                      // this entity.
+  EnumSmallest = 1,   // Enum is smallest container big enough to hold all
+                      // values.
+  Enum32Bit = 2,      // Enum is at least 32 bits.
+  Enum32BitABI = 3,   // Every enumeration visible across an ABI-complying
+                      // interface contains a value needing 32 bits to encode
+                      // it; other enums can be containerized.
+
   // Tag_ABI_HardFP_use, (=27), uleb128
   HardFPImplied = 0,          // FP use should be implied by Tag_FP_arch
   HardFPSinglePrecision = 1,  // Single-precision only

lib/Target/ARM/ARMAsmPrinter.cpp

@@ -730,6 +730,32 @@ void ARMAsmPrinter::emitAttributes() {
   if (Subtarget->hasDivideInARMMode() && !Subtarget->hasV8Ops())
       ATS.emitAttribute(ARMBuildAttrs::DIV_use, ARMBuildAttrs::AllowDIVExt);
 
+  if (MMI) {
+    if (const Module *SourceModule = MMI->getModule()) {
+      // ABI_PCS_wchar_t to indicate wchar_t width
+      // FIXME: There is no way to emit value 0 (wchar_t prohibited).
+      if (auto WCharWidthValue = cast_or_null<ConstantInt>(
+              SourceModule->getModuleFlag("wchar_size"))) {
+        int WCharWidth = WCharWidthValue->getZExtValue();
+        assert((WCharWidth == 2 || WCharWidth == 4) &&
+               "wchar_t width must be 2 or 4 bytes");
+        ATS.emitAttribute(ARMBuildAttrs::ABI_PCS_wchar_t, WCharWidth);
+      }
+
+      // ABI_enum_size to indicate enum width
+      // FIXME: There is no way to emit value 0 (enums prohibited) or value 3
+      //        (all enums contain a value needing 32 bits to encode).
+      if (auto EnumWidthValue = cast_or_null<ConstantInt>(
+              SourceModule->getModuleFlag("min_enum_size"))) {
+        int EnumWidth = EnumWidthValue->getZExtValue();
+        assert((EnumWidth == 1 || EnumWidth == 4) &&
+               "Minimum enum width must be 1 or 4 bytes");
+        int EnumBuildAttr = EnumWidth == 1 ? 1 : 2;
+        ATS.emitAttribute(ARMBuildAttrs::ABI_enum_size, EnumBuildAttr);
+      }
+    }
+  }
+
   if (Subtarget->hasTrustZone() && Subtarget->hasVirtualization())
       ATS.emitAttribute(ARMBuildAttrs::Virtualization_use,
                         ARMBuildAttrs::AllowTZVirtualization);

test/CodeGen/ARM/metadata-default.ll

@@ -0,0 +1,16 @@
+; RUN: llc < %s -mtriple=armv7-linux-gnueabi | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-n32-S64"
+target triple = "armv7--none-eabi"
+
+define i32 @f(i64 %z) {
+	ret i32 0
+}
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = metadata !{i32 1, metadata !"wchar_size", i32 4}
+!1 = metadata !{i32 1, metadata !"min_enum_size", i32 4}
+
+; CHECK: .eabi_attribute 18, 4   @ Tag_ABI_PCS_wchar_t
+; CHECK: .eabi_attribute 26, 2   @ Tag_ABI_enum_size

test/CodeGen/ARM/metadata-short-enums.ll

@@ -0,0 +1,16 @@
+; RUN: llc < %s | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-n32-S64"
+target triple = "armv7--none-eabi"
+
+define i32 @f(i64 %z) {
+	ret i32 0
+}
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = metadata !{i32 1, metadata !"wchar_size", i32 4}
+!1 = metadata !{i32 1, metadata !"min_enum_size", i32 1}
+
+; CHECK: .eabi_attribute 18, 4   @ Tag_ABI_PCS_wchar_t
+; CHECK: .eabi_attribute 26, 1   @ Tag_ABI_enum_size

test/CodeGen/ARM/metadata-short-wchar.ll

@@ -0,0 +1,16 @@
+; RUN: llc < %s | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-n32-S64"
+target triple = "armv7--none-eabi"
+
+define i32 @f(i64 %z) {
+	ret i32 0
+}
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = metadata !{i32 1, metadata !"wchar_size", i32 2}
+!1 = metadata !{i32 1, metadata !"min_enum_size", i32 4}
+
+; CHECK: .eabi_attribute 18, 2   @ Tag_ABI_PCS_wchar_t
+; CHECK: .eabi_attribute 26, 2   @ Tag_ABI_enum_size