Add materialization of virtual base registers for frame indices allocated into

the local block. Resolve references to those indices to a new base register.
For simplification and testing purposes, a new virtual base register is
allocated for each frame index being resolved. The result is truly horrible,
but correct, code that's good for exercising the new code paths.

Next up is adding thumb1 support, which should be very simple. Following that
will be adding base register re-use and implementing a reasonable ARM
heuristic for when a virtual base register should be generated at all.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111315 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 26 insertions, 2 deletions

diff --git a/lib/CodeGen/LocalStackSlotAllocation.cpp b/lib/CodeGen/LocalStackSlotAllocation.cpp
index 065cf80ca4..3927beec11 100644
--- a/lib/CodeGen/LocalStackSlotAllocation.cpp
+++ b/lib/CodeGen/LocalStackSlotAllocation.cpp
@@ -27,6 +27,7 @@
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -160,6 +161,14 @@ void LocalStackSlotPass::insertFrameReferenceRegisters(MachineFunction &Fn) {
          E = Fn.end(); BB != E; ++BB) {
     for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
       MachineInstr *MI = I;
+      // Debug value instructions can't be out of range, so they don't need
+      // any updates.
+      // FIXME: When we extend this stuff to handle functions with both
+      // VLAs and dynamic realignment, we should update the debug values
+      // to reference the new base pointer when possible.
+      if (MI->isDebugValue())
+        continue;
+
       // For now, allocate the base register(s) within the basic block
       // where they're used, and don't try to keep them around outside
       // of that. It may be beneficial to try sharing them more broadly
@@ -169,8 +178,12 @@ void LocalStackSlotPass::insertFrameReferenceRegisters(MachineFunction &Fn) {
       for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
         // Consider replacing all frame index operands that reference
         // an object allocated in the local block.
-        if (MI->getOperand(i).isFI() &&
-            MFI->isObjectPreAllocated(MI->getOperand(i).getIndex())) {
+        if (MI->getOperand(i).isFI()) {
+          int FrameIdx = MI->getOperand(i).getIndex();
+          // Don't try this with values not in the local block.
+          if (!MFI->isObjectPreAllocated(FrameIdx))
+            continue;
+
           DEBUG(dbgs() << "Considering: " << *MI);
           if (TRI->needsFrameBaseReg(MI, i)) {
             DEBUG(dbgs() << "  Replacing FI in: " << *MI);
@@ -182,6 +195,17 @@ void LocalStackSlotPass::insertFrameReferenceRegisters(MachineFunction &Fn) {
             // create a new one.
             // FIXME: For the moment, just always create a new one.
 
+            const TargetRegisterClass *RC = TRI->getPointerRegClass();
+            unsigned BaseReg = Fn.getRegInfo().createVirtualRegister(RC);
+
+            // Tell the target to insert the instruction to initialize
+            // the base register.
+            TRI->materializeFrameBaseRegister(I, BaseReg, FrameIdx);
+
+            // Modify the instruction to use the new base register rather
+            // than the frame index operand.
+            TRI->resolveFrameIndex(I, BaseReg, 0);
+
             ++NumBaseRegisters;
             ++NumReplacements;
           }