From 6009751244909c277e6cee8e74a4ccf1846953bc Mon Sep 17 00:00:00 2001
From: Jim Grosbach <grosbach@apple.com>
Date: Mon, 19 Oct 2009 22:57:03 +0000
Subject: [PATCH] Enable allocation of R3 in Thumb1

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84563 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/ARM/ARMBaseRegisterInfo.cpp   | 6 ++----
 lib/Target/ARM/ARMRegisterInfo.td        | 5 +----
 lib/Target/ARM/README-Thumb.txt          | 8 --------
 lib/Target/ARM/Thumb1RegisterInfo.cpp    | 1 -
 test/CodeGen/Thumb/2009-08-20-ISelBug.ll | 2 +-
 5 files changed, 4 insertions(+), 18 deletions(-)

diff --git a/lib/Target/ARM/ARMBaseRegisterInfo.cpp b/lib/Target/ARM/ARMBaseRegisterInfo.cpp
index 42ef183e526..9f3bdca6f7d 100644
--- a/lib/Target/ARM/ARMBaseRegisterInfo.cpp
+++ b/lib/Target/ARM/ARMBaseRegisterInfo.cpp
@@ -740,8 +740,7 @@ unsigned ARMBaseRegisterInfo::getRegisterPairEven(unsigned Reg,
   case ARM::R1:
     return ARM::R0;
   case ARM::R3:
-    // FIXME!
-    return STI.isThumb1Only() ? 0 : ARM::R2;
+    return ARM::R2;
   case ARM::R5:
     return ARM::R4;
   case ARM::R7:
@@ -830,8 +829,7 @@ unsigned ARMBaseRegisterInfo::getRegisterPairOdd(unsigned Reg,
   case ARM::R0:
     return ARM::R1;
   case ARM::R2:
-    // FIXME!
-    return STI.isThumb1Only() ? 0 : ARM::R3;
+    return ARM::R3;
   case ARM::R4:
     return ARM::R5;
   case ARM::R6:
diff --git a/lib/Target/ARM/ARMRegisterInfo.td b/lib/Target/ARM/ARMRegisterInfo.td
index 20a7355b765..e0be7843297 100644
--- a/lib/Target/ARM/ARMRegisterInfo.td
+++ b/lib/Target/ARM/ARMRegisterInfo.td
@@ -222,12 +222,9 @@ def tGPR : RegisterClass<"ARM", [i32], 32, [R0, R1, R2, R3, R4, R5, R6, R7]> {
     iterator allocation_order_begin(const MachineFunction &MF) const;
     iterator allocation_order_end(const MachineFunction &MF) const;
   }];
-  // FIXME: We are reserving r3 in Thumb mode in case the PEI needs to use it
-  // to generate large stack offset. Make it available once we have register
-  // scavenging.
   let MethodBodies = [{
     static const unsigned THUMB_tGPR_AO[] = {
-      ARM::R0, ARM::R1, ARM::R2,
+      ARM::R0, ARM::R1, ARM::R2, ARM::R3,
       ARM::R4, ARM::R5, ARM::R6, ARM::R7 };
 
     // FP is R7, only low registers available.
diff --git a/lib/Target/ARM/README-Thumb.txt b/lib/Target/ARM/README-Thumb.txt
index a961a576f40..e7770b2292e 100644
--- a/lib/Target/ARM/README-Thumb.txt
+++ b/lib/Target/ARM/README-Thumb.txt
@@ -196,14 +196,6 @@ This is especially bad when dynamic alloca is used. The all fixed size stack
 objects are referenced off the frame pointer with negative offsets. See
 oggenc for an example.
 
-//===---------------------------------------------------------------------===//
-
-We are reserving R3 as a scratch register under thumb mode. So if it is live in
-to the function, we save / restore R3 to / from R12. Until register scavenging
-is done, we should save R3 to a high callee saved reg at emitPrologue time
-(when hasFP is true or stack size is large) and restore R3 from that register
-instead. This allows us to at least get rid of the save to r12 everytime it is
-used.
 
 //===---------------------------------------------------------------------===//
 
diff --git a/lib/Target/ARM/Thumb1RegisterInfo.cpp b/lib/Target/ARM/Thumb1RegisterInfo.cpp
index 33537883dc4..7e1fc572df6 100644
--- a/lib/Target/ARM/Thumb1RegisterInfo.cpp
+++ b/lib/Target/ARM/Thumb1RegisterInfo.cpp
@@ -845,7 +845,6 @@ void Thumb1RegisterInfo::emitEpilogue(MachineFunction &MF,
 
   if (VARegSaveSize) {
     // Epilogue for vararg functions: pop LR to R3 and branch off it.
-    // FIXME: Verify this is still ok when R3 is no longer being reserved.
     AddDefaultPred(BuildMI(MBB, MBBI, dl, TII.get(ARM::tPOP)))
       .addReg(0) // No write back.
       .addReg(ARM::R3, RegState::Define);
diff --git a/test/CodeGen/Thumb/2009-08-20-ISelBug.ll b/test/CodeGen/Thumb/2009-08-20-ISelBug.ll
index 1627f61b39a..c31b65b54e3 100644
--- a/test/CodeGen/Thumb/2009-08-20-ISelBug.ll
+++ b/test/CodeGen/Thumb/2009-08-20-ISelBug.ll
@@ -11,7 +11,7 @@
 
 define arm_apcscc i32 @t(%struct.asl_file_t* %s, i64 %off, i64* %out) nounwind optsize {
 ; CHECK: t:
-; CHECK: adds r4, #8
+; CHECK: adds r3, #8
 entry:
   %val = alloca i64, align 4                      ; <i64*> [#uses=3]
   %0 = icmp eq %struct.asl_file_t* %s, null       ; <i1> [#uses=1]