CodeGenModule: Always output wchar_size; check LLVM assumptions.

[MatzeB]

Summary

llvm::TargetLibraryInfo needs to know the size of wchar_t to work on
functions like wcslen. This patch changes clang to always emit the
wchar_size module flag (it would only do so for ARM previously).
This also adds an assert() to ensure the LLVM defaults based on the
target triple are in sync with clang.

[efriedma]

This makes sense to me, but I'll wait to see if anyone else has a comment.

test/CodeGen/wchar-size.c

3

Maybe add a comment to the test noting that -fno-short-wchar has no effect on Windows.

[rnk]

This seems like the kind of thing we would normally express in DataLayout.

[MatzeB]

In D32982#749215, @rnk wrote:

This seems like the kind of thing we would normally express in DataLayout.

As far as I can tell DataLayout is designed to talk about llvm types (llvm::Type), talking about types/typedefs at the source language level seems out of scope.

[MatzeB]

ping. Do we really need wchar_t size in DataLayout to move this forward? I'm not convinced that is the right place for it...

[MatzeB]

Add comment to test

[rnk]

I guess this is better than DataLayout. Also, the user experience of mixing two TUs with different -fshort-wchar settings during LTO is better.

lib/CodeGen/CodeGenModule.cpp

473

Is this what clang-format does?

lib/CodeGen/CodeGenModule.cpp

 #include "clang/Basic/Module.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/Version.h"
 #include "clang/CodeGen/ConstantInitBuilder.h"
 #include "clang/Frontend/CodeGenOptions.h"
 #include "clang/Sema/SemaDiagnostic.h"
 #include "llvm/ADT/Triple.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/CallingConv.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/ProfileData/InstrProfReader.h"
 #include "llvm/Support/ConvertUTF.h"
void CodeGenModule::Release() {
   }
   if (DebugInfo)
     // We support a single version in the linked module. The LLVM
     // parser will drop debug info with a different version number
     // (and warn about it, too).
     getModule().addModuleFlag(llvm::Module::Warning, "Debug Info Version",
                               llvm::DEBUG_METADATA_VERSION);
 
+  // Width of wchar_t in bytes
+  uint64_t WCharWidth =
+      Context.getTypeSizeInChars(Context.getWideCharType()).getQuantity();
+  assert(LangOpts.ShortWChar ||
+         llvm::TargetLibraryInfoImpl::getTargetWCharSize(Target.getTriple())
+         == Target.getWCharWidth()/8 && "LLVM wchar_t size out of sync");
+
   // We need to record the widths of enums and wchar_t, so that we can generate
-  // the correct build attributes in the ARM backend.
+  // the correct build attributes in the ARM backend. wchar_size is also used by
+  // TargetLibraryInfo.
+  getModule().addModuleFlag(llvm::Module::Error, "wchar_size", WCharWidth);
+
   llvm::Triple::ArchType Arch = Context.getTargetInfo().getTriple().getArch();
   if (   Arch == llvm::Triple::arm
       || Arch == llvm::Triple::armeb
       || Arch == llvm::Triple::thumb
       || Arch == llvm::Triple::thumbeb) {
-    // Width of wchar_t in bytes
-    uint64_t WCharWidth =
-        Context.getTypeSizeInChars(Context.getWideCharType()).getQuantity();
-    getModule().addModuleFlag(llvm::Module::Error, "wchar_size", WCharWidth);
-
     // The minimum width of an enum in bytes
     uint64_t EnumWidth = Context.getLangOpts().ShortEnums ? 1 : 4;
     getModule().addModuleFlag(llvm::Module::Error, "min_enum_size", EnumWidth);
   }
 
   if (CodeGenOpts.SanitizeCfiCrossDso) {
     // Indicate that we want cross-DSO control flow integrity checks.
     getModule().addModuleFlag(llvm::Module::Override, "Cross-DSO CFI", 1);

test/CodeGen/wchar-size.c

+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -o - %s | FileCheck %s -check-prefix=LONG-WCHAR
+// RUN: %clang_cc1 -triple x86_64-unknown-windows-msvc -emit-llvm -o - %s | FileCheck %s -check-prefix=SHORT-WCHAR
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -o - -fshort-wchar %s | FileCheck %s -check-prefix=SHORT-WCHAR
+// Note: -fno-short-wchar implies the target default is used; so there is no
+// need to test this separately here.
+
+// LONG-WCHAR: !{{[0-9]+}} = !{i32 {{[0-9]+}}, !"wchar_size", i32 4}
+// SHORT-WCHAR: !{{[0-9]+}} = !{i32 {{[0-9]+}}, !"wchar_size", i32 2}