add ARM cmd line option to force always using virtual base regs when possible.

Intended to help ease reproducing problems by increasing base register usage
after heuristics for only using the when needed are in place.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111930 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 16 insertions, 4 deletions

diff --git a/lib/Target/ARM/ARMBaseRegisterInfo.cpp b/lib/Target/ARM/ARMBaseRegisterInfo.cpp
index 1408e34..cf6507b 100644
--- a/lib/Target/ARM/ARMBaseRegisterInfo.cpp
+++ b/lib/Target/ARM/ARMBaseRegisterInfo.cpp
@@ -43,6 +43,9 @@ namespace llvm {
 cl::opt<bool>
 ReuseFrameIndexVals("arm-reuse-frame-index-vals", cl::Hidden, cl::init(true),
           cl::desc("Reuse repeated frame index values"));
+cl::opt<bool>
+ForceAllBaseRegAlloc("arm-force-base-reg-alloc", cl::Hidden, cl::init(true),
+          cl::desc("Force use of virtual base registers for stack load/store"));
 }
 
 using namespace llvm;
@@ -1436,10 +1439,9 @@ needsFrameBaseReg(MachineInstr *MI, unsigned operand) const {
   // we don't know everything for certain yet) whether this offset is likely
   // to be out of range of the immediate. Return true if so.
 
-  // FIXME: For testing, return true for all loads/stores and false for
-  // everything else. We want to create lots of base regs to shake out bugs.
+  // We only generate virtual base registers for loads and stores, so
+  // return false for everything else.
   unsigned Opc = MI->getOpcode();
-
   switch (Opc) {
   case ARM::LDR: case ARM::LDRH: case ARM::LDRB:
   case ARM::STR: case ARM::STRH: case ARM::STRB:
@@ -1448,10 +1450,20 @@ needsFrameBaseReg(MachineInstr *MI, unsigned operand) const {
   case ARM::VLDRS: case ARM::VLDRD:
   case ARM::VSTRS: case ARM::VSTRD:
   case ARM::tSTRspi: case ARM::tLDRspi:
-    return true;
+    if (ForceAllBaseRegAlloc)
+      return true;
+    break;
   default:
     return false;
   }
+
+  // FIXME: TODO
+  // Without a virtual base register, if the function has variable sized
+  // objects, all fixed-size local references will be via the frame pointer,
+  // otherwise via the stack pointer. Approximate the offset and see if it's
+  // legal for the instruction.
+
+  return true;
 }
 
 /// materializeFrameBaseRegister - Insert defining instruction(s) for