From a4e6397fd9f2fbbd6affdfb0738813918cb21da0 Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Mon, 25 Jun 2012 18:18:27 +0000
Subject: [PATCH] Enforce stricter liveness rules for PHIs.

Verify that all paths from the entry block to a virtual register read
pass through a def. Enable this check even when MRI->isSSA() is false.

Verify that the live range of a virtual register is live out of all
predecessor blocks, even for PHI-values.

This requires that PHIElimination sometimes inserts IMPLICIT_DEF
instruction in predecessor blocks.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159150 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/MachineVerifier.cpp   | 17 +++++++++++------
 test/CodeGen/Generic/undef-phi.ll | 26 ++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 6 deletions(-)
 create mode 100644 test/CodeGen/Generic/undef-phi.ll

diff --git a/lib/CodeGen/MachineVerifier.cpp b/lib/CodeGen/MachineVerifier.cpp
index 92d9356e83b..a443b51d15e 100644
--- a/lib/CodeGen/MachineVerifier.cpp
+++ b/lib/CodeGen/MachineVerifier.cpp
@@ -1049,7 +1049,7 @@ void MachineVerifier::visitMachineFunctionAfter() {
   // Now check liveness info if available
   calcRegsRequired();
 
-  if (MRI->isSSA() && !MF->empty()) {
+  if (!MF->empty()) {
     BBInfo &MInfo = MBBInfoMap[&MF->front()];
     for (RegSet::iterator
          I = MInfo.vregsRequired.begin(), E = MInfo.vregsRequired.end(); I != E;
@@ -1332,15 +1332,18 @@ void MachineVerifier::verifyLiveIntervals() {
           ++MFI;
           continue;
         }
+
+        // Is VNI a PHI-def in the current block?
+        bool IsPHI = VNI->isPHIDef() &&
+                     VNI->def == LiveInts->getMBBStartIdx(MFI);
+
         // Check that VNI is live-out of all predecessors.
         for (MachineBasicBlock::const_pred_iterator PI = MFI->pred_begin(),
              PE = MFI->pred_end(); PI != PE; ++PI) {
           SlotIndex PEnd = LiveInts->getMBBEndIdx(*PI);
           const VNInfo *PVNI = LI.getVNInfoBefore(PEnd);
 
-          if (VNI->isPHIDef() && VNI->def == LiveInts->getMBBStartIdx(MFI))
-            continue;
-
+          // All predecessors must have a live-out value.
           if (!PVNI) {
             report("Register not marked live out of predecessor", *PI);
             *OS << "Valno #" << VNI->id << " live into BB#" << MFI->getNumber()
@@ -1349,12 +1352,14 @@ void MachineVerifier::verifyLiveIntervals() {
             continue;
           }
 
-          if (PVNI != VNI) {
+          // Only PHI-defs can take different predecessor values.
+          if (!IsPHI && PVNI != VNI) {
             report("Different value live out of predecessor", *PI);
             *OS << "Valno #" << PVNI->id << " live out of BB#"
                 << (*PI)->getNumber() << '@' << PEnd
                 << "\nValno #" << VNI->id << " live into BB#" << MFI->getNumber()
-                << '@' << LiveInts->getMBBStartIdx(MFI) << " in " << LI << '\n';
+                << '@' << LiveInts->getMBBStartIdx(MFI) << " in "
+                << PrintReg(Reg) << ": " << LI << '\n';
           }
         }
         if (&*MFI == EndMBB)
diff --git a/test/CodeGen/Generic/undef-phi.ll b/test/CodeGen/Generic/undef-phi.ll
new file mode 100644
index 00000000000..10899f9fa2d
--- /dev/null
+++ b/test/CodeGen/Generic/undef-phi.ll
@@ -0,0 +1,26 @@
+; RUN: llc < %s -verify-machineinstrs -verify-coalescing
+;
+; This function has a PHI with one undefined input. Verify that PHIElimination
+; inserts an IMPLICIT_DEF instruction in the predecessor so all paths to the use
+; pass through a def.
+
+%struct.xx_stack = type { i32, %struct.xx_stack* }
+
+define i32 @push(%struct.xx_stack* %stack) nounwind uwtable readonly ssp {
+entry:
+  %tobool1 = icmp eq %struct.xx_stack* %stack, null
+  br i1 %tobool1, label %for.end, label %for.body
+
+for.body:
+  %stack.addr.02 = phi %struct.xx_stack* [ %0, %for.body ], [ %stack, %entry ]
+  %next = getelementptr inbounds %struct.xx_stack* %stack.addr.02, i64 0, i32 1
+  %0 = load %struct.xx_stack** %next, align 8
+  %tobool = icmp eq %struct.xx_stack* %0, null
+  br i1 %tobool, label %for.end, label %for.body
+
+for.end:
+  %top.0.lcssa = phi %struct.xx_stack* [ undef, %entry ], [ %stack.addr.02, %for.body ]
+  %first = getelementptr inbounds %struct.xx_stack* %top.0.lcssa, i64 0, i32 0
+  %1 = load i32* %first, align 4
+  ret i32 %1
+}