Use logarithmic units for basic block alignment.

This was actually a bit of a mess. TLI.setPrefLoopAlignment was clearly
documented as taking log2(bytes) units, but the x86 target would still
set a preferred loop alignment of '16'.

CodePlacementOpt passed this number on to the basic block, and
AsmPrinter interpreted it as bytes.

Now both MachineFunction and MachineBasicBlock use logarithmic
alignments.

Obviously, MachineConstantPool still measures alignments in bytes, so we
can emulate the thrill of using as.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145889 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/CodeGen/MachineBasicBlock.h b/include/llvm/CodeGen/MachineBasicBlock.h
index 5a20e952b9cc41cf25b595a91a6b5f641c6792de..499f62d660f772669c2f6542d366822f898ebc7c 100644 (file)
--- a/include/llvm/CodeGen/MachineBasicBlock.h
+++ b/include/llvm/CodeGen/MachineBasicBlock.h
@@ -84,8 +84,9 @@ class MachineBasicBlock : public ilist_node<MachineBasicBlock> {
 
   /// Alignment - Alignment of the basic block. Zero if the basic block does
   /// not need to be aligned.
+  /// The alignment is specified as log2(bytes).
   unsigned Alignment;
-  
+
   /// IsLandingPad - Indicate that this basic block is entered via an
   /// exception handler.
   bool IsLandingPad;
@@ -219,10 +220,12 @@ public:
   bool            livein_empty() const { return LiveIns.empty(); }
 
   /// getAlignment - Return alignment of the basic block.
+  /// The alignment is specified as log2(bytes).
   ///
   unsigned getAlignment() const { return Alignment; }
 
   /// setAlignment - Set alignment of the basic block.
+  /// The alignment is specified as log2(bytes).
   ///
   void setAlignment(unsigned Align) { Alignment = Align; }
 

diff --git a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index d60a1f1e0a549be47b017a2132471194335dc711..8c69a3aca819e891ab63011e63a90791a81aadb1 100644 (file)
--- a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -1970,7 +1970,7 @@ static void EmitBasicBlockLoopComments(const MachineBasicBlock &MBB,
 void AsmPrinter::EmitBasicBlockStart(const MachineBasicBlock *MBB) const {
   // Emit an alignment directive for this block, if needed.
   if (unsigned Align = MBB->getAlignment())
-    EmitAlignment(Log2_32(Align));
+    EmitAlignment(Align);
 
   // If the block has its address taken, emit any labels that were used to
   // reference the block.  It is possible that there is more than one label

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index a67d27568d01dd313b4e6458758c0f95ceaac8ad..a214c06c3b524f7d8dd3d5e85c0348ce8ef2d282 100644 (file)
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -1211,10 +1211,10 @@ X86TargetLowering::X86TargetLowering(X86TargetMachine &TM)
   maxStoresPerMemcpyOptSize = Subtarget->isTargetDarwin() ? 8 : 4;
   maxStoresPerMemmove = 8; // For @llvm.memmove -> sequence of stores
   maxStoresPerMemmoveOptSize = Subtarget->isTargetDarwin() ? 8 : 4;
-  setPrefLoopAlignment(16);
+  setPrefLoopAlignment(4); // 2^4 bytes.
   benefitFromCodePlacementOpt = true;
 
-  setPrefFunctionAlignment(4);
+  setPrefFunctionAlignment(4); // 2^4 bytes.
 }