Making use of VFP / NEON floating point multiply-accumulate / subtraction is

difficult on current ARM implementations for a few reasons.
1. Even though a single vmla has latency that is one cycle shorter than a pair
   of vmul + vadd, a RAW hazard during the first (4? on Cortex-a8) can cause
   additional pipeline stall. So it's frequently better to single codegen
   vmul + vadd.
2. A vmla folowed by a vmul, vmadd, or vsub causes the second fp instruction to
   stall for 4 cycles. We need to schedule them apart.
3. A vmla followed vmla is a special case. Obvious issuing back to back RAW
   vmla + vmla is very bad. But this isn't ideal either:
     vmul
     vadd
     vmla
   Instead, we want to expand the second vmla:
     vmla
     vmul
     vadd
   Even with the 4 cycle vmul stall, the second sequence is still 2 cycles
   faster.

Up to now, isel simply avoid codegen'ing fp vmla / vmls. This works well enough
but it isn't the optimial solution. This patch attempts to make it possible to
use vmla / vmls in cases where it is profitable.

A. Add missing isel predicates which cause vmla to be codegen'ed.
B. Make sure the fmul in (fadd (fmul)) has a single use. We don't want to
   compute a fmul and a fmla.
C. Add additional isel checks for vmla, avoid cases where vmla is feeding into
   fp instructions (except for the #3 exceptional case).
D. Add ARM hazard recognizer to model the vmla / vmls hazards.
E. Add a special pre-regalloc case to expand vmla / vmls when it's likely the
   vmla / vmls will trigger one of the special hazards.

Work in progress, only A+B are enabled.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120960 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 0 insertions, 40 deletions

diff --git a/lib/Target/ARM/Thumb2HazardRecognizer.h b/lib/Target/ARM/Thumb2HazardRecognizer.h
deleted file mode 100644
index aa4411f186..0000000000
--- a/lib/Target/ARM/Thumb2HazardRecognizer.h
+++ /dev/null
@@ -1,40 +0,0 @@
-//===-- Thumb2HazardRecognizer.h - Thumb2 Hazard Recognizers ----*- C++ -*-===//
-//
-//                     The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This file defines hazard recognizers for scheduling Thumb2 functions on
-// ARM processors.
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef THUMB2HAZARDRECOGNIZER_H
-#define THUMB2HAZARDRECOGNIZER_H
-
-#include "llvm/CodeGen/PostRAHazardRecognizer.h"
-
-namespace llvm {
-
-class MachineInstr;
-
-class Thumb2HazardRecognizer : public PostRAHazardRecognizer {
-  unsigned ITBlockSize;  // No. of MIs in current IT block yet to be scheduled.
-  MachineInstr *ITBlockMIs[4];
-
-public:
-  Thumb2HazardRecognizer(const InstrItineraryData *ItinData) :
-    PostRAHazardRecognizer(ItinData) {}
-
-  virtual HazardType getHazardType(SUnit *SU);
-  virtual void Reset();
-  virtual void EmitInstruction(SUnit *SU);
-};
-
-
-} // end namespace llvm
-
-#endif // THUMB2HAZARDRECOGNIZER_H