[LLVM][Alignment] Make functions using log of alignment explicit

Summary:
This patch renames functions that takes or returns alignment as log2, this patch will help with the transition to llvm::Align.
The renaming makes it explicit that we deal with log(alignment) instead of a power of two alignment.
A few renames uncovered dubious assignments:

 - `MirParser`/`MirPrinter` was expecting powers of two but `MachineFunction` and `MachineBasicBlock` were using deal with log2(align). This patch fixes it and updates the documentation.
 - `MachineBlockPlacement` exposes two flags (`align-all-blocks` and `align-all-nofallthru-blocks`) supposedly interpreted as power of two alignments, internally these values are interpreted as log2(align). This patch updates the documentation,
 - `MachineFunctionexposes` exposes `align-all-functions` also interpreted as power of two alignment, internally this value is interpreted as log2(align). This patch updates the documentation,

Reviewers: lattner, thegameg, courbet

Subscribers: dschuff, arsenm, jyknight, dylanmckay, sdardis, nemanjai, jvesely, nhaehnle, javed.absar, hiraditya, kbarton, fedor.sergeev, asb, rbar, johnrusso, simoncook, apazos, sabuasal, niosHD, jrtc27, MaskRay, zzheng, edward-jones, atanasyan, rogfer01, MartinMosbeck, brucehoult, the_o, dexonsmith, PkmX, jocewei, jsji, Jim, s.egerton, llvm-commits, courbet

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65945

llvm-svn: 371045

1 files changed, 9 insertions, 8 deletions

diff --git a/llvm/lib/CodeGen/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index b771dd1a351..d136ebd437f 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -78,10 +78,11 @@ using namespace llvm;
 
 #define DEBUG_TYPE "codegen"
 
-static cl::opt<unsigned>
-AlignAllFunctions("align-all-functions",
-                  cl::desc("Force the alignment of all functions."),
-                  cl::init(0), cl::Hidden);
+static cl::opt<unsigned> AlignAllFunctions(
+    "align-all-functions",
+    cl::desc("Force the alignment of all functions in log2 format (e.g. 4 "
+             "means align on 16B boundaries)."),
+    cl::init(0), cl::Hidden);
 
 static const char *getPropertyName(MachineFunctionProperties::Property Prop) {
   using P = MachineFunctionProperties::Property;
@@ -172,16 +173,16 @@ void MachineFunction::init() {
     FrameInfo->ensureMaxAlignment(F.getFnStackAlignment());
 
   ConstantPool = new (Allocator) MachineConstantPool(getDataLayout());
-  Alignment = STI->getTargetLowering()->getMinFunctionAlignment();
+  LogAlignment = STI->getTargetLowering()->getMinFunctionLogAlignment();
 
   // FIXME: Shouldn't use pref alignment if explicit alignment is set on F.
   // FIXME: Use Function::hasOptSize().
   if (!F.hasFnAttribute(Attribute::OptimizeForSize))
-    Alignment = std::max(Alignment,
-                         STI->getTargetLowering()->getPrefFunctionAlignment());
+    LogAlignment = std::max(
+        LogAlignment, STI->getTargetLowering()->getPrefFunctionLogAlignment());
 
   if (AlignAllFunctions)
-    Alignment = AlignAllFunctions;
+    LogAlignment = AlignAllFunctions;
 
   JumpTableInfo = nullptr;