From 10e412ec6b761952b95710203e6d2d89f4fee53a Mon Sep 17 00:00:00 2001
From: Bill Wendling <isanbard@gmail.com>
Date: Wed, 14 Dec 2011 23:53:24 +0000
Subject: [PATCH] The saved registers weren't being processed in the correct
 order. This lead to the compact unwind claiming that one register was saved
 before another, which isn't all that great in general. Process them in the
 natural order. Reverse the list only when necessary for the algorithm.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146612 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/X86/X86FrameLowering.cpp | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/lib/Target/X86/X86FrameLowering.cpp b/lib/Target/X86/X86FrameLowering.cpp
index 036043637fd..6a40cc17974 100644
--- a/lib/Target/X86/X86FrameLowering.cpp
+++ b/lib/Target/X86/X86FrameLowering.cpp
@@ -351,8 +351,7 @@ void X86FrameLowering::emitCalleeSavedFrameMoves(MachineFunction &MF,
 /// register. The number corresponds to the enum lists in
 /// compact_unwind_encoding.h.
 static int getCompactUnwindRegNum(const unsigned *CURegs, unsigned Reg) {
-  int Idx = 1;
-  for (; *CURegs; ++CURegs, ++Idx)
+  for (int Idx = 1; *CURegs; ++CURegs, ++Idx)
     if (*CURegs == Reg)
       return Idx;
 
@@ -388,12 +387,17 @@ encodeCompactUnwindRegistersWithoutFrame(unsigned SavedRegs[CU_NUM_SAVED_REGS],
   };
   const unsigned *CURegs = (Is64Bit ? CU64BitRegs : CU32BitRegs);
 
-  for (unsigned i = CU_NUM_SAVED_REGS - RegCount; i < CU_NUM_SAVED_REGS; ++i) {
+  for (unsigned i = 0; i != CU_NUM_SAVED_REGS; ++i) {
     int CUReg = getCompactUnwindRegNum(CURegs, SavedRegs[i]);
     if (CUReg == -1) return ~0U;
     SavedRegs[i] = CUReg;
   }
 
+  // Reverse the list.
+  std::swap(SavedRegs[0], SavedRegs[5]);
+  std::swap(SavedRegs[1], SavedRegs[4]);
+  std::swap(SavedRegs[2], SavedRegs[3]);
+
   uint32_t RenumRegs[CU_NUM_SAVED_REGS];
   for (unsigned i = CU_NUM_SAVED_REGS - RegCount; i < CU_NUM_SAVED_REGS; ++i) {
     unsigned Countless = 0;
@@ -454,7 +458,7 @@ encodeCompactUnwindRegistersWithFrame(unsigned SavedRegs[CU_NUM_SAVED_REGS],
   // Encode the registers in the order they were saved, 3-bits per register. The
   // registers are numbered from 1 to 6.
   uint32_t RegEnc = 0;
-  for (int I = 5; I >= 0; --I) {
+  for (int I = 0; I != 6; --I) {
     unsigned Reg = SavedRegs[I];
     if (Reg == 0) break;
     int CURegNum = getCompactUnwindRegNum(CURegs, Reg);
@@ -479,7 +483,7 @@ uint32_t X86FrameLowering::getCompactUnwindEncoding(MachineFunction &MF) const {
   bool HasFP = hasFP(MF);
 
   unsigned SavedRegs[CU_NUM_SAVED_REGS] = { 0, 0, 0, 0, 0, 0 };
-  int SavedRegIdx = CU_NUM_SAVED_REGS;
+  unsigned SavedRegIdx = 0;
 
   unsigned OffsetSize = (Is64Bit ? 8 : 4);
 
@@ -509,9 +513,9 @@ uint32_t X86FrameLowering::getCompactUnwindEncoding(MachineFunction &MF) const {
 
     if (Opc == PushInstr) {
       // If there are too many saved registers, we cannot use compact encoding.
-      if (--SavedRegIdx < 0) return 0;
+      if (SavedRegIdx >= CU_NUM_SAVED_REGS) return 0;
 
-      SavedRegs[SavedRegIdx] = MI.getOperand(0).getReg();
+      SavedRegs[SavedRegIdx++] = MI.getOperand(0).getReg();
       StackAdjust += OffsetSize;
       InstrOffset += PushInstrSize;
     } else if (Opc == MoveInstr) {
@@ -523,7 +527,7 @@ uint32_t X86FrameLowering::getCompactUnwindEncoding(MachineFunction &MF) const {
 
       StackAdjust = 0;
       memset(SavedRegs, 0, sizeof(SavedRegs));
-      SavedRegIdx = CU_NUM_SAVED_REGS;
+      SavedRegIdx = 0;
       InstrOffset += MoveInstrSize;
     } else if (Opc == X86::SUB64ri32 || Opc == X86::SUB64ri8 ||
                Opc == X86::SUB32ri || Opc == X86::SUB32ri8) {
@@ -586,13 +590,12 @@ uint32_t X86FrameLowering::getCompactUnwindEncoding(MachineFunction &MF) const {
     }
 
     // Encode the number of registers saved.
-    CompactUnwindEncoding |= ((CU_NUM_SAVED_REGS - SavedRegIdx) & 0x7) << 10;
+    CompactUnwindEncoding |= (SavedRegIdx & 0x7) << 10;
 
     // Get the encoding of the saved registers when we don't have a frame
     // pointer.
     uint32_t RegEnc =
-      encodeCompactUnwindRegistersWithoutFrame(SavedRegs,
-                                               CU_NUM_SAVED_REGS - SavedRegIdx,
+      encodeCompactUnwindRegistersWithoutFrame(SavedRegs, SavedRegIdx,
                                                Is64Bit);
     if (RegEnc == ~0U) return 0;
 
-- 
2.34.1