Correct PPC FRAMEADDR lowering using a pseudo-register

The old code used to lower FRAMEADDR tried to replicate the logic in the real
frame-lowering code that determines whether or not the frame pointer (r31) will
be used. When it seemed as through the frame pointer would not be used, the
stack pointer (r1) was used instead. Unfortunately, because the stack size is
not yet known, this does not work. Instead, this change introduces new
always-reserved pseudo-registers (FP and FP8) that are replaced during prologue
insertion with the real frame-pointer register (either r1 or r31).

It is important that this intrinsic always return a valid frame address because
it is used by Clang to store the frame address as part of code generation for
__builtin_setjmp.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177653 91177308-0d34-0410-b5e6-96231b3b80d8

6 files changed, 97 insertions, 9 deletions

diff --git a/lib/Target/PowerPC/PPCFrameLowering.cpp b/lib/Target/PowerPC/PPCFrameLowering.cpp
index 353560d7f9..0108f7256e 100644
--- a/lib/Target/PowerPC/PPCFrameLowering.cpp
+++ b/lib/Target/PowerPC/PPCFrameLowering.cpp
@@ -299,6 +299,31 @@ bool PPCFrameLowering::needsFP(const MachineFunction &MF) const {
      MF.getInfo<PPCFunctionInfo>()->hasFastCall());
 }
 
+void PPCFrameLowering::replaceFPWithRealFP(MachineFunction &MF) const {
+  bool is31 = needsFP(MF);
+  unsigned FPReg  = is31 ? PPC::R31 : PPC::R1;
+  unsigned FP8Reg = is31 ? PPC::X31 : PPC::X1;
+
+  for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
+       BI != BE; ++BI)
+    for (MachineBasicBlock::iterator MBBI = BI->end(); MBBI != BI->begin(); ) {
+      --MBBI;
+      for (unsigned I = 0, E = MBBI->getNumOperands(); I != E; ++I) {
+        MachineOperand &MO = MBBI->getOperand(I);
+        if (!MO.isReg())
+          continue;
+
+        switch (MO.getReg()) {
+        case PPC::FP:
+          MO.setReg(FPReg);
+          break;
+        case PPC::FP8:
+          MO.setReg(FP8Reg);
+          break;
+        }
+      }
+    }
+}
 
 void PPCFrameLowering::emitPrologue(MachineFunction &MF) const {
   MachineBasicBlock &MBB = MF.front();   // Prolog goes in entry BB
@@ -332,6 +357,9 @@ void PPCFrameLowering::emitPrologue(MachineFunction &MF) const {
   unsigned FrameSize = determineFrameLayout(MF);
   int NegFrameSize = -FrameSize;
 
+  if (MFI->isFrameAddressTaken())
+    replaceFPWithRealFP(MF);
+
   // Get processor type.
   bool isPPC64 = Subtarget.isPPC64();
   // Get operating system
diff --git a/lib/Target/PowerPC/PPCFrameLowering.h b/lib/Target/PowerPC/PPCFrameLowering.h
index 53ee32601f..6f5f9368c6 100644
--- a/lib/Target/PowerPC/PPCFrameLowering.h
+++ b/lib/Target/PowerPC/PPCFrameLowering.h
@@ -43,6 +43,7 @@ public:
 
   bool hasFP(const MachineFunction &MF) const;
   bool needsFP(const MachineFunction &MF) const;
+  void replaceFPWithRealFP(MachineFunction &MF) const;
 
   void processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
                                             RegScavenger *RS = NULL) const;
diff --git a/lib/Target/PowerPC/PPCISelLowering.cpp b/lib/Target/PowerPC/PPCISelLowering.cpp
index c50811d52b..72cb6f535a 100644
--- a/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -6815,13 +6815,16 @@ SDValue PPCTargetLowering::LowerFRAMEADDR(SDValue Op,
   MachineFunction &MF = DAG.getMachineFunction();
   MachineFrameInfo *MFI = MF.getFrameInfo();
   MFI->setFrameAddressIsTaken(true);
-  bool is31 = (getTargetMachine().Options.DisableFramePointerElim(MF) ||
-               MFI->hasVarSizedObjects()) &&
-                  MFI->getStackSize() &&
-                  !MF.getFunction()->getAttributes().
-                    hasAttribute(AttributeSet::FunctionIndex, Attribute::Naked);
-  unsigned FrameReg = isPPC64 ? (is31 ? PPC::X31 : PPC::X1) :
-                                (is31 ? PPC::R31 : PPC::R1);
+
+  // Naked functions never have a frame pointer, and so we use r1. For all
+  // other functions, this decision must be delayed until during PEI.
+  unsigned FrameReg;
+  if (MF.getFunction()->getAttributes().hasAttribute(
+        AttributeSet::FunctionIndex, Attribute::Naked))
+    FrameReg = isPPC64 ? PPC::X1 : PPC::R1;
+  else
+    FrameReg = isPPC64 ? PPC::FP8 : PPC::FP;
+
   SDValue FrameAddr = DAG.getCopyFromReg(DAG.getEntryNode(), dl, FrameReg,
                                          PtrVT);
   while (Depth--)
diff --git a/lib/Target/PowerPC/PPCRegisterInfo.cpp b/lib/Target/PowerPC/PPCRegisterInfo.cpp
index bd7d285431..9b860062e8 100644
--- a/lib/Target/PowerPC/PPCRegisterInfo.cpp
+++ b/lib/Target/PowerPC/PPCRegisterInfo.cpp
@@ -114,6 +114,11 @@ BitVector PPCRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   // when used in instructions that treat r0 as the constant 0.
   Reserved.set(PPC::ZERO);
 
+  // The FP register is also not really a register, but is the representation
+  // of the frame pointer register used by ISD::FRAMEADDR.
+  Reserved.set(PPC::FP);
+  Reserved.set(PPC::FP8);
+
   Reserved.set(PPC::R0);
   Reserved.set(PPC::R1);
   Reserved.set(PPC::LR);
diff --git a/lib/Target/PowerPC/PPCRegisterInfo.td b/lib/Target/PowerPC/PPCRegisterInfo.td
index 34623b6dc9..e91bf7fe5d 100644
--- a/lib/Target/PowerPC/PPCRegisterInfo.td
+++ b/lib/Target/PowerPC/PPCRegisterInfo.td
@@ -89,6 +89,10 @@ foreach Index = 0-31 in {
 // The reprsentation of r0 when treated as the constant 0.
 def ZERO : GPR<0, "r0">;
 
+// Representations of the frame pointer used by ISD::FRAMEADDR.
+def FP   : GPR<0 /* arbitrary */, "**FRAME POINTER**">;
+def FP8  : GP8<FP, "**FRAME POINTER**">;
+
 // Condition register bits
 def CR0LT : CRBIT< 0, "0">;
 def CR0GT : CRBIT< 1, "1">;
@@ -167,11 +171,11 @@ def RM: SPR<512, "**ROUNDING MODE**">;
 // then nonvolatiles in reverse order since stmw/lmw save from rN to r31
 def GPRC : RegisterClass<"PPC", [i32], 32, (add (sequence "R%u", 2, 12),
                                                 (sequence "R%u", 30, 13),
-                                                R31, R0, R1, LR)>;
+                                                R31, R0, R1, LR, FP)>;
 
 def G8RC : RegisterClass<"PPC", [i64], 64, (add (sequence "X%u", 2, 12),
                                                 (sequence "X%u", 30, 14),
-                                                X31, X13, X0, X1, LR8)>;
+                                                X31, X13, X0, X1, LR8, FP8)>;
 
 // For some instructions r0 is special (representing the value 0 instead of
 // the value in the r0 register), and we use these register subclasses to
diff --git a/test/CodeGen/PowerPC/frameaddr.ll b/test/CodeGen/PowerPC/frameaddr.ll
new file mode 100644
index 0000000000..eabd4a68aa
--- /dev/null
+++ b/test/CodeGen/PowerPC/frameaddr.ll
@@ -0,0 +1,47 @@
+; RUN: llc < %s -mcpu=pwr7 | FileCheck %s
+target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f128:128:128-v128:128:128-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+declare void @llvm.eh.sjlj.longjmp(i8*) #1
+
+define i8* @main() #0 {
+entry:
+  %0 = call i8* @llvm.frameaddress(i32 0)
+  ret i8* %0
+
+; CHECK: @main
+; CHECK: mr 3, 1
+}
+
+define i8* @foo() #3 { ; naked
+entry:
+  %0 = call i8* @llvm.frameaddress(i32 0)
+  ret i8* %0
+
+; CHECK: @foo
+; CHECK: mr 3, 1
+}
+
+define i8* @bar() #0 {
+entry:
+  %x = alloca [100000 x i8]                       ; <[100000 x i8]*> [#uses=1]
+  %x1 = bitcast [100000 x i8]* %x to i8*          ; <i8*> [#uses=1]
+  call void @use(i8* %x1) nounwind
+  %0 = call i8* @llvm.frameaddress(i32 0)
+  ret i8* %0
+
+; Note that if we start eliminating non-leaf frame pointers by default, this
+; will need to be updated.
+; CHECK: @bar
+; CHECK: mr 3, 31
+}
+
+declare void @use(i8*)
+
+declare i8* @llvm.frameaddress(i32) #2
+
+attributes #0 = { nounwind "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-frame-pointer-elim-non-leaf"="true" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { noreturn nounwind }
+attributes #2 = { nounwind readnone }
+attributes #3 = { nounwind naked "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-frame-pointer-elim-non-leaf"="true" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "unsafe-fp-math"="false" "use-soft-float"="false" }
+