[X86] Use the correct alignment for COMDAT constant pool entries

COFF doesn't have sections with mergeable contents.  Instead, each
constant pool entry ends up in a COMDAT section.  The linker, when
choosing between COMDAT sections, doesn't choose the max alignment of
the two sections.  You just get whatever alignment was on the section.

If one constant needed a higher alignment in one object file from
another one, then we will get into trouble if the linker chooses the
lower alignment one.

Instead, lets promote the alignment of the constant pool entry to make
sure we don't use an under aligned constant with an instruction which
assumed otherwise.

This fixes PR26680.

llvm-svn: 261462

6 files changed, 36 insertions, 15 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 4d945bdcc76..47f21b36b65 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -1194,9 +1194,10 @@ bool AsmPrinter::doFinalization(Module &M) {
 
   // Emit __morestack address if needed for indirect calls.
   if (MMI->usesMorestackAddr()) {
+    unsigned Align = 1;
     MCSection *ReadOnlySection = getObjFileLowering().getSectionForConstant(
         getDataLayout(), SectionKind::getReadOnly(),
-        /*C=*/nullptr);
+        /*C=*/nullptr, Align);
     OutStreamer->SwitchSection(ReadOnlySection);
 
     MCSymbol *AddrSymbol =
@@ -1286,8 +1287,8 @@ void AsmPrinter::EmitConstantPool() {
     if (!CPE.isMachineConstantPoolEntry())
       C = CPE.Val.ConstVal;
 
-    MCSection *S =
-        getObjFileLowering().getSectionForConstant(getDataLayout(), Kind, C);
+    MCSection *S = getObjFileLowering().getSectionForConstant(getDataLayout(),
+                                                              Kind, C, Align);
 
     // The number of sections are small, just do a linear search from the
     // last section to the first.
diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 5dfdb7acef1..81b429a8d11 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -351,7 +351,8 @@ bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(
 /// Given a mergeable constant with the specified size and relocation
 /// information, return a section that it should be placed in.
 MCSection *TargetLoweringObjectFileELF::getSectionForConstant(
-    const DataLayout &DL, SectionKind Kind, const Constant *C) const {
+    const DataLayout &DL, SectionKind Kind, const Constant *C,
+    unsigned &Align) const {
   if (Kind.isMergeableConst4() && MergeableConst4Section)
     return MergeableConst4Section;
   if (Kind.isMergeableConst8() && MergeableConst8Section)
@@ -636,7 +637,8 @@ MCSection *TargetLoweringObjectFileMachO::SelectSectionForGlobal(
 }
 
 MCSection *TargetLoweringObjectFileMachO::getSectionForConstant(
-    const DataLayout &DL, SectionKind Kind, const Constant *C) const {
+    const DataLayout &DL, SectionKind Kind, const Constant *C,
+    unsigned &Align) const {
   // If this constant requires a relocation, we have to put it in the data
   // segment, not in the text segment.
   if (Kind.isData() || Kind.isReadOnlyWithRel())
diff --git a/llvm/lib/Target/TargetLoweringObjectFile.cpp b/llvm/lib/Target/TargetLoweringObjectFile.cpp
index a0b0d8f2404..3c04a214fad 100644
--- a/llvm/lib/Target/TargetLoweringObjectFile.cpp
+++ b/llvm/lib/Target/TargetLoweringObjectFile.cpp
@@ -252,8 +252,10 @@ TargetLoweringObjectFile::SectionForGlobal(const GlobalValue *GV,
 
 MCSection *TargetLoweringObjectFile::getSectionForJumpTable(
     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
+  unsigned Align = 0;
   return getSectionForConstant(F.getParent()->getDataLayout(),
-                               SectionKind::getReadOnly(), /*C=*/nullptr);
+                               SectionKind::getReadOnly(), /*C=*/nullptr,
+                               Align);
 }
 
 bool TargetLoweringObjectFile::shouldPutJumpTableInFunctionSection(
@@ -277,7 +279,8 @@ bool TargetLoweringObjectFile::shouldPutJumpTableInFunctionSection(
 /// Given a mergable constant with the specified size and relocation
 /// information, return a section that it should be placed in.
 MCSection *TargetLoweringObjectFile::getSectionForConstant(
-    const DataLayout &DL, SectionKind Kind, const Constant *C) const {
+    const DataLayout &DL, SectionKind Kind, const Constant *C,
+    unsigned &Align) const {
   if (Kind.isReadOnly() && ReadOnlySection != nullptr)
     return ReadOnlySection;
 
diff --git a/llvm/lib/Target/X86/X86AsmPrinter.cpp b/llvm/lib/Target/X86/X86AsmPrinter.cpp
index 2170e62e30f..b9513985213 100644
--- a/llvm/lib/Target/X86/X86AsmPrinter.cpp
+++ b/llvm/lib/Target/X86/X86AsmPrinter.cpp
@@ -568,8 +568,9 @@ MCSymbol *X86AsmPrinter::GetCPISymbol(unsigned CPID) const {
       const DataLayout &DL = MF->getDataLayout();
       SectionKind Kind = CPE.getSectionKind(&DL);
       const Constant *C = CPE.Val.ConstVal;
+      unsigned Align = CPE.Alignment;
       if (const MCSectionCOFF *S = dyn_cast<MCSectionCOFF>(
-              getObjFileLowering().getSectionForConstant(DL, Kind, C))) {
+              getObjFileLowering().getSectionForConstant(DL, Kind, C, Align))) {
         if (MCSymbol *Sym = S->getCOMDATSymbol()) {
           if (Sym->isUndefined())
             OutStreamer->EmitSymbolAttribute(Sym, MCSA_Global);
diff --git a/llvm/lib/Target/X86/X86TargetObjectFile.cpp b/llvm/lib/Target/X86/X86TargetObjectFile.cpp
index 782768d0ab1..0d37fcd1b43 100644
--- a/llvm/lib/Target/X86/X86TargetObjectFile.cpp
+++ b/llvm/lib/Target/X86/X86TargetObjectFile.cpp
@@ -154,16 +154,29 @@ static std::string scalarConstantToHexString(const Constant *C) {
 }
 
 MCSection *X86WindowsTargetObjectFile::getSectionForConstant(
-    const DataLayout &DL, SectionKind Kind, const Constant *C) const {
+    const DataLayout &DL, SectionKind Kind, const Constant *C,
+    unsigned &Align) const {
   if (Kind.isMergeableConst() && C) {
     const unsigned Characteristics = COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                                      COFF::IMAGE_SCN_MEM_READ |
                                      COFF::IMAGE_SCN_LNK_COMDAT;
     std::string COMDATSymName;
-    if (Kind.isMergeableConst4() || Kind.isMergeableConst8())
-      COMDATSymName = "__real@" + scalarConstantToHexString(C);
-    else if (Kind.isMergeableConst16())
-      COMDATSymName = "__xmm@" + scalarConstantToHexString(C);
+    if (Kind.isMergeableConst4()) {
+      if (Align <= 4) {
+        COMDATSymName = "__real@" + scalarConstantToHexString(C);
+        Align = 4;
+      }
+    } else if (Kind.isMergeableConst8()) {
+      if (Align <= 8) {
+        COMDATSymName = "__real@" + scalarConstantToHexString(C);
+        Align = 8;
+      }
+    } else if (Kind.isMergeableConst16()) {
+      if (Align <= 16) {
+        COMDATSymName = "__xmm@" + scalarConstantToHexString(C);
+        Align = 16;
+      }
+    }
 
     if (!COMDATSymName.empty())
       return getContext().getCOFFSection(".rdata", Characteristics, Kind,
@@ -171,5 +184,5 @@ MCSection *X86WindowsTargetObjectFile::getSectionForConstant(
                                          COFF::IMAGE_COMDAT_SELECT_ANY);
   }
 
-  return TargetLoweringObjectFile::getSectionForConstant(DL, Kind, C);
+  return TargetLoweringObjectFile::getSectionForConstant(DL, Kind, C, Align);
 }
diff --git a/llvm/lib/Target/X86/X86TargetObjectFile.h b/llvm/lib/Target/X86/X86TargetObjectFile.h
index 6b2448cc9de..81207ad6304 100644
--- a/llvm/lib/Target/X86/X86TargetObjectFile.h
+++ b/llvm/lib/Target/X86/X86TargetObjectFile.h
@@ -59,7 +59,8 @@ namespace llvm {
     /// \brief Given a mergeable constant with the specified size and relocation
     /// information, return a section that it should be placed in.
     MCSection *getSectionForConstant(const DataLayout &DL, SectionKind Kind,
-                                     const Constant *C) const override;
+                                     const Constant *C,
+                                     unsigned &Align) const override;
   };
 
 } // end namespace llvm