From ce10f185554b03518bd58b63461fbbcfff733909 Mon Sep 17 00:00:00 2001
From: Reed Kotler <rkotler@mips.com>
Date: Thu, 21 Nov 2013 05:13:23 +0000
Subject: [PATCH] Add, to constant islands, long jumps similar to ARM far
 branch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195312 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/Mips/Mips16InstrInfo.td         |  1 +
 lib/Target/Mips/MipsConstantIslandPass.cpp | 24 ++++++++++++--
 test/CodeGen/Mips/mbrsize4a.ll             | 37 ++++++++++++++++++++++
 3 files changed, 60 insertions(+), 2 deletions(-)
 create mode 100644 test/CodeGen/Mips/mbrsize4a.ll

diff --git a/lib/Target/Mips/Mips16InstrInfo.td b/lib/Target/Mips/Mips16InstrInfo.td
index 7441c78a033..7f2d925f4f0 100644
--- a/lib/Target/Mips/Mips16InstrInfo.td
+++ b/lib/Target/Mips/Mips16InstrInfo.td
@@ -734,6 +734,7 @@ def DivuRxRy16: FRR16_div_ins<0b11011, "divu", IIAlu> {
 def Jal16 : FJAL16_ins<0b0, "jal", IIAlu> {
   let hasDelaySlot = 0;  // not true, but we add the nop for now
   let isCall=1;
+  let Defs = [RA];
 }
 
 //
diff --git a/lib/Target/Mips/MipsConstantIslandPass.cpp b/lib/Target/Mips/MipsConstantIslandPass.cpp
index c46bbacf658..63d07f35478 100644
--- a/lib/Target/Mips/MipsConstantIslandPass.cpp
+++ b/lib/Target/Mips/MipsConstantIslandPass.cpp
@@ -1399,9 +1399,29 @@ bool
 MipsConstantIslands::fixupUnconditionalBr(ImmBranch &Br) {
   MachineInstr *MI = Br.MI;
   MachineBasicBlock *MBB = MI->getParent();
+  MachineBasicBlock *DestBB = MI->getOperand(0).getMBB();
   // Use BL to implement far jump.
-  Br.MaxDisp = ((1 << 16)-1) * 2;
-  MI->setDesc(TII->get(Mips::BimmX16));
+  unsigned BimmX16MaxDisp = ((1 << 16)-1) * 2;
+  if (isBBInRange(MI, DestBB, BimmX16MaxDisp)) {
+    Br.MaxDisp = BimmX16MaxDisp;
+    MI->setDesc(TII->get(Mips::BimmX16));
+  }
+  else {
+    // need to give the math a more careful look here
+    // this is really a segment address and not
+    // a PC relative address. FIXME. But I think that
+    // just reducing the bits by 1 as I've done is correct.
+    // The basic block we are branching too much be longword aligned.
+    // we know that RA is saved because we always save it right now.
+    // this requirement will be relaxed later but we also have an alternate
+    // way to implement this that I will implement that does not need jal.
+    // We should have a way to back out this alignment restriction if we "can" later.
+    // but it is not harmful.
+    //
+    DestBB->setAlignment(2);
+    Br.MaxDisp = ((1<<24)-1) * 2;
+    MI->setDesc(TII->get(Mips::Jal16));
+  }
   BBInfo[MBB->getNumber()].Size += 2;
   adjustBBOffsetsAfter(MBB);
   HasFarJump = true;
diff --git a/test/CodeGen/Mips/mbrsize4a.ll b/test/CodeGen/Mips/mbrsize4a.ll
new file mode 100644
index 00000000000..c80299166ab
--- /dev/null
+++ b/test/CodeGen/Mips/mbrsize4a.ll
@@ -0,0 +1,37 @@
+; RUN: llc -mtriple=mipsel-linux-gnu -march=mipsel -mcpu=mips16 -soft-float -mips16-hard-float -relocation-model=static -mips16-constant-islands   < %s | FileCheck %s -check-prefix=jal16
+
+@j = global i32 10, align 4
+@.str = private unnamed_addr constant [11 x i8] c"at bottom\0A\00", align 1
+@i = common global i32 0, align 4
+
+; Function Attrs: nounwind
+define i32 @main() #0 {
+entry:
+  %retval = alloca i32, align 4
+  store i32 0, i32* %retval
+  br label %z
+
+z:                                                ; preds = %y, %entry
+  %call = call i32 bitcast (i32 (...)* @foo to i32 ()*)()
+  call void asm sideeffect ".space 10000000", ""() #2, !srcloc !1
+  br label %y
+
+y:                                                ; preds = %z
+  %call1 = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([11 x i8]* @.str, i32 0, i32 0))
+  br label %z
+
+return:                                           ; No predecessors!
+  %0 = load i32* %retval
+  ret i32 %0
+; jal16: 	jal	$BB{{[0-9]+}}_{{[0-9]+}}
+}
+
+declare i32 @foo(...) #1
+
+declare i32 @printf(i8*, ...) #1
+
+attributes #0 = { nounwind "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { nounwind }
+
+!1 = metadata !{i32 68}