Rework global alignment computation again. Now we do round up

alignment of globals to the preferred alignment, but only when
there is no section specified on the global (by far the common
case).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@102515 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/AsmPrinter.h

@@ -204,12 +204,8 @@ namespace llvm {
     /// EmitAlignment - Emit an alignment directive to the specified power of
     /// two boundary.  For example, if you pass in 3 here, you will get an 8
     /// byte alignment.  If a global value is specified, and if that global has
-    /// an explicit alignment requested, it will unconditionally override the
+    /// an explicit alignment requested, it will override the alignment request
-    /// alignment request.
+    /// if required for correctness.
-    ///
-    /// The algorithm is:
-    ///     Align = NumBits;
-    ///     if (GV && GV->hasalignment) Align = GV->getAlignment();
     ///
     void EmitAlignment(unsigned NumBits, const GlobalValue *GV = 0) const;
     
@@ -218,7 +214,6 @@ namespace llvm {
     /// it if appropriate.
     void EmitBasicBlockStart(const MachineBasicBlock *MBB) const;
     
-    
     /// EmitGlobalConstant - Print a general LLVM constant to the .s file.
     void EmitGlobalConstant(const Constant *CV, unsigned AddrSpace = 0);
     

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -61,6 +61,35 @@ static gcp_map_type &getGCMap(void *&P) {
 }
 
 
+/// getGVAlignmentLog2 - Return the alignment to use for the specified global
+/// value in log2 form.  This rounds up to the preferred alignment if possible
+/// and legal.
+static unsigned getGVAlignmentLog2(const GlobalValue *GV, const TargetData &TD,
+                                   unsigned InBits = 0) {
+  unsigned NumBits = 0;
+  if (const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV))
+    NumBits = TD.getPreferredAlignmentLog(GVar);
+  
+  // If InBits is specified, round it to it.
+  if (InBits > NumBits)
+    NumBits = InBits;
+  
+  // If the GV has a specified alignment, take it into account.
+  if (GV->getAlignment() == 0)
+    return NumBits;
+  
+  unsigned GVAlign = Log2_32(GV->getAlignment());
+  
+  // If the GVAlign is larger than NumBits, or if we are required to obey
+  // NumBits because the GV has an assigned section, obey it.
+  if (GVAlign > NumBits || GV->hasSection())
+    NumBits = GVAlign;
+  return NumBits;
+}
+
+
+
+
 AsmPrinter::AsmPrinter(TargetMachine &tm, MCStreamer &Streamer)
   : MachineFunctionPass(&ID),
     TM(tm), MAI(tm.getMCAsmInfo()),
@@ -227,16 +256,12 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
   SectionKind GVKind = TargetLoweringObjectFile::getKindForGlobal(GV, TM);
 
   const TargetData *TD = TM.getTargetData();
-  unsigned Size = TD->getTypeAllocSize(GV->getType()->getElementType());
+  uint64_t Size = TD->getTypeAllocSize(GV->getType()->getElementType());
   
   // If the alignment is specified, we *must* obey it.  Overaligning a global
   // with a specified alignment is a prompt way to break globals emitted to
   // sections and expected to be contiguous (e.g. ObjC metadata).
-  unsigned AlignLog;
+  unsigned AlignLog = getGVAlignmentLog2(GV, *TD);
-  if (unsigned GVAlign = GV->getAlignment())
-    AlignLog = Log2_32(GVAlign);
-  else
-    AlignLog = TD->getPreferredAlignmentLog(GV);
   
   // Handle common and BSS local symbols (.lcomm).
   if (GVKind.isCommon() || GVKind.isBSSLocal()) {
@@ -1010,7 +1035,7 @@ bool AsmPrinter::EmitSpecialLLVMGlobal(const GlobalVariable *GV) {
   unsigned Align = Log2_32(TD->getPointerPrefAlignment());
   if (GV->getName() == "llvm.global_ctors") {
     OutStreamer.SwitchSection(getObjFileLowering().getStaticCtorSection());
-    EmitAlignment(Align, 0);
+    EmitAlignment(Align);
     EmitXXStructorList(GV->getInitializer());
     
     if (TM.getRelocationModel() == Reloc::Static &&
@@ -1024,7 +1049,7 @@ bool AsmPrinter::EmitSpecialLLVMGlobal(const GlobalVariable *GV) {
   
   if (GV->getName() == "llvm.global_dtors") {
     OutStreamer.SwitchSection(getObjFileLowering().getStaticDtorSection());
-    EmitAlignment(Align, 0);
+    EmitAlignment(Align);
     EmitXXStructorList(GV->getInitializer());
 
     if (TM.getRelocationModel() == Reloc::Static &&
@@ -1153,20 +1178,13 @@ void AsmPrinter::EmitLabelOffsetDifference(const MCSymbol *Hi, uint64_t Offset,
 // EmitAlignment - Emit an alignment directive to the specified power of
 // two boundary.  For example, if you pass in 3 here, you will get an 8
 // byte alignment.  If a global value is specified, and if that global has
-// an explicit alignment requested, it will unconditionally override the
+// an explicit alignment requested, it will override the alignment request
-// alignment request.  However, if ForcedAlignBits is specified, this value
+// if required for correctness.
-// has final say: the ultimate alignment will be the max of ForcedAlignBits
-// and the alignment computed with NumBits and the global.
-//
-// The algorithm is:
-//     Align = NumBits;
-//     if (GV && GV->hasalignment) Align = GV->getAlignment();
 //
 void AsmPrinter::EmitAlignment(unsigned NumBits, const GlobalValue *GV) const {
-  if (GV && GV->getAlignment())
+  if (GV) NumBits = getGVAlignmentLog2(GV, *TM.getTargetData(), NumBits);
-    NumBits = Log2_32(GV->getAlignment());
   
-  if (NumBits == 0) return;   // No need to emit alignment.
+  if (NumBits == 0) return;   // 1-byte aligned: no need to emit alignment.
   
   if (getCurrentSection()->getKind().isText())
     OutStreamer.EmitCodeAlignment(1 << NumBits);

test/CodeGen/X86/alignment.ll

@@ -6,7 +6,7 @@
 
 ; CHECK:	.bss
 ; CHECK:	.globl	GlobalA
-; CHECK:	.align	8
+; CHECK:	.align	16
 ; CHECK: GlobalA:
 ; CHECK:	.zero	384
 
@@ -15,4 +15,29 @@
 ; PR6921
 @GlobalB = common global { [384 x i8] } zeroinitializer, align 8
 
-; CHECK: 	.comm	GlobalB,384,8
+; CHECK: 	.comm	GlobalB,384,16
+
+
+@GlobalC = common global { [384 x i8] } zeroinitializer, align 2
+
+; CHECK: 	.comm	GlobalC,384,16
+
+
+
+; This cannot get rounded up to the preferred alignment (16) if they have an
+; explicit alignment specified *and* a section specified.
+@GlobalAS = global { [384 x i8] } zeroinitializer, align 8, section "foo"
+
+; CHECK:	.globl	GlobalAS
+; CHECK:	.align	8
+; CHECK: GlobalAS:
+; CHECK:	.zero	384
+
+; Common variables should not get rounded up to the preferred alignment (16) if
+; they have an explicit alignment specified and a section specified.
+; PR6921
+@GlobalBS = common global { [384 x i8] } zeroinitializer, align 8, section "foo"
+; CHECK: 	.comm	GlobalBS,384,8
+
+@GlobalCS = common global { [384 x i8] } zeroinitializer, align 2, section "foo"
+; CHECK: 	.comm	GlobalCS,384,2

test/CodeGen/X86/unaligned-load.ll

@@ -29,8 +29,8 @@ return:
 declare void @llvm.memcpy.i64(i8* nocapture, i8* nocapture, i64, i32) nounwind
 
 ; CORE2: .section
-; CORE2: .align  3
+; CORE2: .align  4
 ; CORE2-NEXT: _.str1:
 ; CORE2-NEXT: .asciz "DHRYSTONE PROGRAM, SOME STRING"
-; CORE2: .align 3
+; CORE2: .align 4
 ; CORE2-NEXT: _.str3:

test/FrontendC/cstring-align.c

@@ -1,6 +1,5 @@
 // RUN: %llvmgcc %s -c -Os -m32 -emit-llvm -o - | llc -march=x86 -mtriple=i386-apple-darwin10 | FileCheck %s -check-prefix=DARWIN32
 // RUN: %llvmgcc %s -c -Os -m64 -emit-llvm -o - | llc -march=x86-64 -mtriple=x86_64-apple-darwin10 | FileCheck %s -check-prefix=DARWIN64
-// XFAIL: *
 // XTARGET: darwin
 
 extern void func(const char *, const char *);
@@ -9,10 +8,10 @@ void long_function_name() {
   func("%s: the function name", __func__);
 }
 
-// DARWIN64: .align 3
+// DARWIN64: .align 4
 // DARWIN64: ___func__.
 // DARWIN64: .asciz "long_function_name"
 
-// DARWIN32: .align 2
+// DARWIN32: .align 4
 // DARWIN32: ___func__.
 // DARWIN32: .asciz "long_function_name"