This refactoring of ARM machine block size computation creates two utility

functions so that the size computation is available not only in ConstantIslands
but in other passes as well.

Differential Revision: https://reviews.llvm.org/D22640

llvm-svn: 276399

1 files changed, 72 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/ARMComputeBlockSize.cpp b/llvm/lib/Target/ARM/ARMComputeBlockSize.cpp
new file mode 100644
index 00000000000..7c86a6abad4
--- /dev/null
+++ b/llvm/lib/Target/ARM/ARMComputeBlockSize.cpp
@@ -0,0 +1,72 @@
+//===--- ARMComputeBlockSize.cpp - Compute machine block sizes ------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ARM.h"
+#include "ARMBasicBlockInfo.h"
+using namespace llvm;
+
+namespace llvm {
+
+// mayOptimizeThumb2Instruction - Returns true if optimizeThumb2Instructions
+// below may shrink MI.
+static bool
+mayOptimizeThumb2Instruction(const MachineInstr *MI) {
+  switch(MI->getOpcode()) {
+    // optimizeThumb2Instructions.
+    case ARM::t2LEApcrel:
+    case ARM::t2LDRpci:
+    // optimizeThumb2Branches.
+    case ARM::t2B:
+    case ARM::t2Bcc:
+    case ARM::tBcc:
+    // optimizeThumb2JumpTables.
+    case ARM::t2BR_JT:
+      return true;
+  }
+  return false;
+}
+
+void computeBlockSize(MachineFunction *MF, MachineBasicBlock *MBB,
+                      BasicBlockInfo &BBI) {
+  const ARMBaseInstrInfo *TII =
+    static_cast<const ARMBaseInstrInfo *>(MF->getSubtarget().getInstrInfo());
+  bool isThumb = MF->getInfo<ARMFunctionInfo>()->isThumbFunction();
+  BBI.Size = 0;
+  BBI.Unalign = 0;
+  BBI.PostAlign = 0;
+
+  for (MachineInstr &I : *MBB) {
+    BBI.Size += TII->GetInstSizeInBytes(I);
+    // For inline asm, GetInstSizeInBytes returns a conservative estimate.
+    // The actual size may be smaller, but still a multiple of the instr size.
+    if (I.isInlineAsm())
+      BBI.Unalign = isThumb ? 1 : 2;
+    // Also consider instructions that may be shrunk later.
+    else if (isThumb && mayOptimizeThumb2Instruction(&I))
+      BBI.Unalign = 1;
+  }
+
+  // tBR_JTr contains a .align 2 directive.
+  if (!MBB->empty() && MBB->back().getOpcode() == ARM::tBR_JTr) {
+    BBI.PostAlign = 2;
+    MBB->getParent()->ensureAlignment(2);
+  }
+}
+
+std::vector<BasicBlockInfo> computeAllBlockSizes(MachineFunction *MF) {
+  std::vector<BasicBlockInfo> BBInfo;
+  BBInfo.resize(MF->getNumBlockIDs());
+
+  for (MachineBasicBlock &MBB : *MF)
+    computeBlockSize(MF, &MBB, BBInfo[MBB.getNumber()]);
+
+  return BBInfo;
+}
+
+} // end namespace