[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

1 files changed, 5 insertions, 2 deletions

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;