From 78dfef771b2552090be60bee404570c2a0b03bcb Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Sat, 25 Oct 2008 00:52:41 +0000
Subject: [PATCH] If val# def is ~0U, meaning it's defined by a PHI, and it's
 previously split, spill before the barrier because it's impossible to
 determine if all the defs are spilled in the same spill slot.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@58129 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/PreAllocSplitting.cpp | 20 +++++++++++---------
 test/CodeGen/X86/pre-split4.ll    | 24 ++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 9 deletions(-)
 create mode 100644 test/CodeGen/X86/pre-split4.ll

diff --git a/lib/CodeGen/PreAllocSplitting.cpp b/lib/CodeGen/PreAllocSplitting.cpp
index 18cac075d88..1b2b635f393 100644
--- a/lib/CodeGen/PreAllocSplitting.cpp
+++ b/lib/CodeGen/PreAllocSplitting.cpp
@@ -527,21 +527,23 @@ bool PreAllocSplitting::SplitRegLiveInterval(LiveInterval *LI) {
   int SS;
   unsigned SpillIndex = 0;
   MachineInstr *SpillMI = NULL;
-  if (isAlreadySplit(CurrLI->reg, ValNo->id, SS)) {
-    // If it's already split, just restore the value. There is no need to spill
-    // the def again.
-  } else if (ValNo->def == ~0U) {
+  bool PrevSpilled = isAlreadySplit(CurrLI->reg, ValNo->id, SS);
+  if (ValNo->def == ~0U) {
     // If it's defined by a phi, we must split just before the barrier.
     MachineBasicBlock::iterator SpillPt = 
       findSpillPoint(BarrierMBB, Barrier, RefsInMBB, SpillIndex);
     if (SpillPt == BarrierMBB->begin())
       return false; // No gap to insert spill.
     // Add spill.
-    SS = MFI->CreateStackObject(RC->getSize(), RC->getAlignment());
+    if (!PrevSpilled)
+      // If previously split, reuse the spill slot.
+      SS = MFI->CreateStackObject(RC->getSize(), RC->getAlignment());
     TII->storeRegToStackSlot(*BarrierMBB, SpillPt, CurrLI->reg, true, SS, RC);
     SpillMI = prior(SpillPt);
     LIs->InsertMachineInstrInMaps(SpillMI, SpillIndex);
-  } else {
+  } else if (!PrevSpilled) {
+    // If it's already split, just restore the value. There is no need to spill
+    // the def again.
     // Check if it's possible to insert a spill after the def MI.
     MachineBasicBlock::iterator SpillPt =
       findNextEmptySlot(DefMBB, DefMI, SpillIndex);
@@ -549,8 +551,8 @@ bool PreAllocSplitting::SplitRegLiveInterval(LiveInterval *LI) {
       return false; // No gap to insert spill.
     SS = MFI->CreateStackObject(RC->getSize(), RC->getAlignment());
 
-    // Add spill. The store instruction kills the register if def is before the
-    // barrier in the barrier block.
+    // Add spill. The store instruction kills the register if def is before
+    // the barrier in the barrier block.
     TII->storeRegToStackSlot(*DefMBB, SpillPt, CurrLI->reg,
                              DefMBB == BarrierMBB, SS, RC);
     SpillMI = prior(SpillPt);
@@ -567,7 +569,7 @@ bool PreAllocSplitting::SplitRegLiveInterval(LiveInterval *LI) {
   // If live interval is spilled in the same block as the barrier, just
   // create a hole in the interval.
   if (!DefMBB ||
-      (SpillIndex && SpillMI->getParent() == BarrierMBB)) {
+      (SpillMI && SpillMI->getParent() == BarrierMBB)) {
     UpdateIntervalForSplit(ValNo, LIs->getUseIndex(SpillIndex)+1,
                            LIs->getDefIndex(RestoreIndex));
 
diff --git a/test/CodeGen/X86/pre-split4.ll b/test/CodeGen/X86/pre-split4.ll
new file mode 100644
index 00000000000..44ea375a70e
--- /dev/null
+++ b/test/CodeGen/X86/pre-split4.ll
@@ -0,0 +1,24 @@
+; RUN: llvm-as < %s | llc -march=x86 -mattr=+sse2 -pre-alloc-split -stats |& \
+; RUN:   grep {pre-alloc-split} | grep {Number of intervals split} | grep 4
+
+define i32 @main(i32 %argc, i8** %argv) nounwind {
+entry:
+	br label %bb
+
+bb:		; preds = %bb, %entry
+	%k.0.reg2mem.0 = phi double [ 1.000000e+00, %entry ], [ %6, %bb ]		; <double> [#uses=2]
+	%Flint.0.reg2mem.0 = phi double [ 0.000000e+00, %entry ], [ %5, %bb ]		; <double> [#uses=1]
+	%twoThrd.0.reg2mem.0 = phi double [ 0.000000e+00, %entry ], [ %1, %bb ]		; <double> [#uses=1]
+	%0 = tail call double @llvm.pow.f64(double 0x3FE5555555555555, double 0.000000e+00)		; <double> [#uses=1]
+	%1 = add double %0, %twoThrd.0.reg2mem.0		; <double> [#uses=1]
+	%2 = tail call double @sin(double %k.0.reg2mem.0) nounwind readonly		; <double> [#uses=1]
+	%3 = mul double 0.000000e+00, %2		; <double> [#uses=1]
+	%4 = fdiv double 1.000000e+00, %3		; <double> [#uses=1]
+	%5 = add double %4, %Flint.0.reg2mem.0		; <double> [#uses=1]
+	%6 = add double %k.0.reg2mem.0, 1.000000e+00		; <double> [#uses=1]
+	br label %bb
+}
+
+declare double @llvm.pow.f64(double, double) nounwind readonly
+
+declare double @sin(double) nounwind readonly
-- 
2.34.1