From db42d51ee36c479511df56310bb5c2e079df7702 Mon Sep 17 00:00:00 2001
From: Martin Storsjo <martin@martin.st>
Date: Mon, 23 Jul 2018 22:15:25 +0000
Subject: [PATCH] [MC] Add a separate flag for skipping comdat constant
 sections for MinGW. NFC.

This actually has nothing to do with the associative comdat sections
that aren't supported by GNU binutils ld.

Clarify the comments from SVN r335918 and use a separate flag for it.

Differential Revision: https://reviews.llvm.org/D49645

llvm-svn: 337757
---
 llvm/include/llvm/MC/MCAsmInfo.h                  | 5 +++++
 llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp | 8 +++++---
 llvm/lib/MC/MCAsmInfoCOFF.cpp                     | 8 ++++++++
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/llvm/include/llvm/MC/MCAsmInfo.h b/llvm/include/llvm/MC/MCAsmInfo.h
index 0a0f37966fc5..120fb8fa7492 100644
--- a/llvm/include/llvm/MC/MCAsmInfo.h
+++ b/llvm/include/llvm/MC/MCAsmInfo.h
@@ -89,6 +89,10 @@ protected:
   /// them.
   bool HasCOFFAssociativeComdats = false;
 
+  /// True if this is a non-GNU COFF target. For GNU targets, we don't generate
+  /// constants into comdat sections.
+  bool HasCOFFComdatConstants = false;
+
   /// This is the maximum possible length of an instruction, which is needed to
   /// compute the size of an inline asm.  Defaults to 4.
   unsigned MaxInstLength = 4;
@@ -469,6 +473,7 @@ public:
   bool hasMachoZeroFillDirective() const { return HasMachoZeroFillDirective; }
   bool hasMachoTBSSDirective() const { return HasMachoTBSSDirective; }
   bool hasCOFFAssociativeComdats() const { return HasCOFFAssociativeComdats; }
+  bool hasCOFFComdatConstants() const { return HasCOFFComdatConstants; }
   unsigned getMaxInstLength() const { return MaxInstLength; }
   unsigned getMinInstAlignment() const { return MinInstAlignment; }
   bool getDollarIsPC() const { return DollarIsPC; }
diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index b726b21f6b99..b5dd2d4cca89 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -1397,9 +1397,11 @@ MCSection *TargetLoweringObjectFileCOFF::getSectionForConstant(
     const DataLayout &DL, SectionKind Kind, const Constant *C,
     unsigned &Align) const {
   if (Kind.isMergeableConst() && C &&
-      getContext().getAsmInfo()->hasCOFFAssociativeComdats()) {
-    // GNU binutils doesn't support the kind of symbol with a null
-    // storage class that this generates.
+      getContext().getAsmInfo()->hasCOFFComdatConstants()) {
+    // This creates comdat sections with the given symbol name, but unless
+    // AsmPrinter::GetCPISymbol actually makes the symbol global, the symbol
+    // will be created with a null storage class, which makes GNU binutils
+    // error out.
     const unsigned Characteristics = COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                                      COFF::IMAGE_SCN_MEM_READ |
                                      COFF::IMAGE_SCN_LNK_COMDAT;
diff --git a/llvm/lib/MC/MCAsmInfoCOFF.cpp b/llvm/lib/MC/MCAsmInfoCOFF.cpp
index 8bb02c3f649c..d8fb875b67c6 100644
--- a/llvm/lib/MC/MCAsmInfoCOFF.cpp
+++ b/llvm/lib/MC/MCAsmInfoCOFF.cpp
@@ -45,6 +45,11 @@ MCAsmInfoCOFF::MCAsmInfoCOFF() {
   // If this is a COFF target, assume that it supports associative comdats. It's
   // part of the spec.
   HasCOFFAssociativeComdats = true;
+
+  // We can generate constants in comdat sections that can be shared,
+  // but in order not to create null typed symbols, we actually need to
+  // make them global symbols as well.
+  HasCOFFComdatConstants = true;
 }
 
 void MCAsmInfoMicrosoft::anchor() {}
@@ -58,4 +63,7 @@ MCAsmInfoGNUCOFF::MCAsmInfoGNUCOFF() {
   // comdats for jump tables, unwind information, and other data associated with
   // a function.
   HasCOFFAssociativeComdats = false;
+
+  // We don't create constants in comdat sections for MinGW.
+  HasCOFFComdatConstants = false;
 }