[clang, SystemZ] Support -munaligned-symbols (#73511)

When this option is passed to clang, external (and/or weak) symbols
are not assumed to have the minimum ABI alignment normally required.
Symbols defined locally that are not weak are however still given the
minimum alignment.

This is implemented by passing a new parameter to getMinGlobalAlign()
named HasNonWeakDef that is used to return the right alignment value.

This is needed when external symbols created from a linker script may
not get the ABI minimum alignment and must therefore be treated as
unaligned by the compiler.

Author: JonPsson1

clang/include/clang/AST/ASTContext.h

@@ -2413,12 +2413,18 @@ class ASTContext : public RefCountedBase<ASTContext> {
   unsigned getTargetDefaultAlignForAttributeAligned() const;
 
   /// Return the alignment in bits that should be given to a
-  /// global variable with type \p T.
-  unsigned getAlignOfGlobalVar(QualType T) const;
+  /// global variable with type \p T. If \p VD is non-null it will be
+  /// considered specifically for the query.
+  unsigned getAlignOfGlobalVar(QualType T, const VarDecl *VD) const;
 
   /// Return the alignment in characters that should be given to a
-  /// global variable with type \p T.
-  CharUnits getAlignOfGlobalVarInChars(QualType T) const;
+  /// global variable with type \p T. If \p VD is non-null it will be
+  /// considered specifically for the query.
+  CharUnits getAlignOfGlobalVarInChars(QualType T, const VarDecl *VD) const;
+
+  /// Return the minimum alignement as specified by the target. If \p VD is
+  /// non-null it may be used to identify external or weak variables.
+  unsigned getMinGlobalAlignOfVar(uint64_t Size, const VarDecl *VD) const;
 
   /// Return a conservative estimate of the alignment of the specified
   /// decl \p D.

clang/include/clang/Basic/TargetInfo.h

@@ -704,8 +704,10 @@ class TargetInfo : public TransferrableTargetInfo,
   }
 
   /// getMinGlobalAlign - Return the minimum alignment of a global variable,
-  /// unless its alignment is explicitly reduced via attributes.
-  virtual unsigned getMinGlobalAlign (uint64_t) const {
+  /// unless its alignment is explicitly reduced via attributes. If \param
+  /// HasNonWeakDef is true, this concerns a VarDecl which has a definition
+  /// in current translation unit and that is not weak.
+  virtual unsigned getMinGlobalAlign(uint64_t Size, bool HasNonWeakDef) const {
     return MinGlobalAlign;
   }
 

clang/include/clang/Driver/Options.td

@@ -4619,6 +4619,10 @@ def munaligned_access : Flag<["-"], "munaligned-access">, Group<m_Group>,
   HelpText<"Allow memory accesses to be unaligned (AArch32/AArch64/LoongArch/RISC-V only)">;
 def mno_unaligned_access : Flag<["-"], "mno-unaligned-access">, Group<m_Group>,
   HelpText<"Force all memory accesses to be aligned (AArch32/AArch64/LoongArch/RISC-V only)">;
+def munaligned_symbols : Flag<["-"], "munaligned-symbols">, Group<m_Group>,
+  HelpText<"Expect external char-aligned symbols to be without ABI alignment (SystemZ only)">;
+def mno_unaligned_symbols : Flag<["-"], "mno-unaligned-symbols">, Group<m_Group>,
+  HelpText<"Expect external char-aligned symbols to be without ABI alignment (SystemZ only)">;
 } // let Flags = [TargetSpecific]
 def mstrict_align : Flag<["-"], "mstrict-align">, Alias<mno_unaligned_access>,
   Flags<[HelpHidden]>, Visibility<[ClangOption, CC1Option]>,

clang/lib/AST/ASTContext.cpp

@@ -1688,7 +1688,7 @@ CharUnits ASTContext::getDeclAlign(const Decl *D, bool ForAlignof) const {
       if (VD->hasGlobalStorage() && !ForAlignof) {
         uint64_t TypeSize =
             !BaseT->isIncompleteType() ? getTypeSize(T.getTypePtr()) : 0;
-        Align = std::max(Align, getTargetInfo().getMinGlobalAlign(TypeSize));
+        Align = std::max(Align, getMinGlobalAlignOfVar(TypeSize, VD));
       }
 
     // Fields can be subject to extra alignment constraints, like if
@@ -2511,16 +2511,25 @@ unsigned ASTContext::getTargetDefaultAlignForAttributeAligned() const {
 
 /// getAlignOfGlobalVar - Return the alignment in bits that should be given
 /// to a global variable of the specified type.
-unsigned ASTContext::getAlignOfGlobalVar(QualType T) const {
+unsigned ASTContext::getAlignOfGlobalVar(QualType T, const VarDecl *VD) const {
   uint64_t TypeSize = getTypeSize(T.getTypePtr());
   return std::max(getPreferredTypeAlign(T),
-                  getTargetInfo().getMinGlobalAlign(TypeSize));
+                  getMinGlobalAlignOfVar(TypeSize, VD));
 }
 
 /// getAlignOfGlobalVarInChars - Return the alignment in characters that
 /// should be given to a global variable of the specified type.
-CharUnits ASTContext::getAlignOfGlobalVarInChars(QualType T) const {
-  return toCharUnitsFromBits(getAlignOfGlobalVar(T));
+CharUnits ASTContext::getAlignOfGlobalVarInChars(QualType T,
+                                                 const VarDecl *VD) const {
+  return toCharUnitsFromBits(getAlignOfGlobalVar(T, VD));
+}
+
+unsigned ASTContext::getMinGlobalAlignOfVar(uint64_t Size,
+                                            const VarDecl *VD) const {
+  // Make the default handling as that of a non-weak definition in the
+  // current translation unit.
+  bool HasNonWeakDef = !VD || (VD->hasDefinition() && !VD->isWeak());
+  return getTargetInfo().getMinGlobalAlign(Size, HasNonWeakDef);
 }
 
 CharUnits ASTContext::getOffsetOfBaseWithVBPtr(const CXXRecordDecl *RD) const {

clang/lib/Basic/Targets/AArch64.cpp

@@ -1517,8 +1517,10 @@ MicrosoftARM64TargetInfo::getCallingConvKind(bool ClangABICompat4) const {
   return CCK_MicrosoftWin64;
 }
 
-unsigned MicrosoftARM64TargetInfo::getMinGlobalAlign(uint64_t TypeSize) const {
-  unsigned Align = WindowsARM64TargetInfo::getMinGlobalAlign(TypeSize);
+unsigned MicrosoftARM64TargetInfo::getMinGlobalAlign(uint64_t TypeSize,
+                                                     bool HasNonWeakDef) const {
+  unsigned Align =
+      WindowsARM64TargetInfo::getMinGlobalAlign(TypeSize, HasNonWeakDef);
 
   // MSVC does size based alignment for arm64 based on alignment section in
   // below document, replicate that to keep alignment consistent with object

clang/lib/Basic/Targets/AArch64.h

@@ -236,7 +236,8 @@ class LLVM_LIBRARY_VISIBILITY MicrosoftARM64TargetInfo
   TargetInfo::CallingConvKind
   getCallingConvKind(bool ClangABICompat4) const override;
 
-  unsigned getMinGlobalAlign(uint64_t TypeSize) const override;
+  unsigned getMinGlobalAlign(uint64_t TypeSize,
+                             bool HasNonWeakDef) const override;
 };
 
 // ARM64 MinGW target

clang/lib/Basic/Targets/CSKY.cpp

@@ -308,7 +308,8 @@ bool CSKYTargetInfo::validateAsmConstraint(
   }
 }
 
-unsigned CSKYTargetInfo::getMinGlobalAlign(uint64_t Size) const {
+unsigned CSKYTargetInfo::getMinGlobalAlign(uint64_t Size,
+                                           bool HasNonWeakDef) const {
   if (Size >= 32)
     return 32;
   return 0;

clang/lib/Basic/Targets/CSKY.h

@@ -71,7 +71,7 @@ class LLVM_LIBRARY_VISIBILITY CSKYTargetInfo : public TargetInfo {
 
   bool isValidCPUName(StringRef Name) const override;
 
-  unsigned getMinGlobalAlign(uint64_t) const override;
+  unsigned getMinGlobalAlign(uint64_t, bool HasNonWeakDef) const override;
 
   ArrayRef<Builtin::Info> getTargetBuiltins() const override;
 

clang/lib/Basic/Targets/NVPTX.cpp

@@ -115,7 +115,8 @@ NVPTXTargetInfo::NVPTXTargetInfo(const llvm::Triple &Triple,
   LongAlign = HostTarget->getLongAlign();
   LongLongWidth = HostTarget->getLongLongWidth();
   LongLongAlign = HostTarget->getLongLongAlign();
-  MinGlobalAlign = HostTarget->getMinGlobalAlign(/* TypeSize = */ 0);
+  MinGlobalAlign = HostTarget->getMinGlobalAlign(/* TypeSize = */ 0,
+                                                 /* HasNonWeakDef = */ true);
   NewAlign = HostTarget->getNewAlign();
   DefaultAlignForAttributeAligned =
       HostTarget->getDefaultAlignForAttributeAligned();

clang/lib/Basic/Targets/SPIR.h

@@ -125,7 +125,9 @@ class LLVM_LIBRARY_VISIBILITY BaseSPIRTargetInfo : public TargetInfo {
       LongAlign = HostTarget->getLongAlign();
       LongLongWidth = HostTarget->getLongLongWidth();
       LongLongAlign = HostTarget->getLongLongAlign();
-      MinGlobalAlign = HostTarget->getMinGlobalAlign(/* TypeSize = */ 0);
+      MinGlobalAlign =
+          HostTarget->getMinGlobalAlign(/* TypeSize = */ 0,
+                                        /* HasNonWeakDef = */ true);
       NewAlign = HostTarget->getNewAlign();
       DefaultAlignForAttributeAligned =
           HostTarget->getDefaultAlignForAttributeAligned();