From bf984670602be7a5fddf3532b7ec6573c590a048 Mon Sep 17 00:00:00 2001
From: Pawel Bylica <chfast@gmail.com>
Date: Wed, 24 Jun 2015 12:49:42 +0000
Subject: [PATCH] Fix instruction scheduling live register tracking

Summary:
This patch fixes PR23405 (https://llvm.org/bugs/show_bug.cgi?id=23405).

During a node unscheduling an entry in LiveRegGens can be replaced with a new value. That corrupts the live reg tracking and LiveReg* structure is not cleared as should be during unscheduling. Problematic condition that enforces Gen replacement is `I->getSUnit()->getHeight() < LiveRegGens[I->getReg()]->getHeight()`. This condition should be checked only if LiveRegGen was set in current node unscheduling.

Test Plan: Regression test included.

Reviewers: hfinkel, atrick

Reviewed By: atrick

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9993

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240538 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../SelectionDAG/ScheduleDAGRRList.cpp        | 25 ++++++++++++------
 test/CodeGen/X86/rrlist-livereg-corrutpion.ll | 26 +++++++++++++++++++
 2 files changed, 43 insertions(+), 8 deletions(-)
 create mode 100644 test/CodeGen/X86/rrlist-livereg-corrutpion.ll

diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
index fd0fa31842b..12ca59ff18c 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
@@ -848,17 +848,26 @@ void ScheduleDAGRRList::UnscheduleNodeBottomUp(SUnit *SU) {
       }
     }
 
-  for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
-       I != E; ++I) {
-    if (I->isAssignedRegDep()) {
-      if (!LiveRegDefs[I->getReg()])
+  for (auto &Succ : SU->Succs) {
+    if (Succ.isAssignedRegDep()) {
+      auto Reg = Succ.getReg();
+      if (!LiveRegDefs[Reg])
         ++NumLiveRegs;
       // This becomes the nearest def. Note that an earlier def may still be
       // pending if this is a two-address node.
-      LiveRegDefs[I->getReg()] = SU;
-      if (LiveRegGens[I->getReg()] == nullptr ||
-          I->getSUnit()->getHeight() < LiveRegGens[I->getReg()]->getHeight())
-        LiveRegGens[I->getReg()] = I->getSUnit();
+      LiveRegDefs[Reg] = SU;
+
+      // Update LiveRegGen only if was empty before this unscheduling.
+      // This is to avoid incorrect updating LiveRegGen set in previous run.
+      if (!LiveRegGens[Reg]) {
+        // Find the successor with the lowest height.
+        LiveRegGens[Reg] = Succ.getSUnit();
+        for (auto &Succ2 : SU->Succs) {
+          if (Succ2.isAssignedRegDep() && Succ2.getReg() == Reg &&
+              Succ2.getSUnit()->getHeight() < LiveRegGens[Reg]->getHeight())
+            LiveRegGens[Reg] = Succ2.getSUnit();
+        }
+      }
     }
   }
   if (SU->getHeight() < MinAvailableCycle)
diff --git a/test/CodeGen/X86/rrlist-livereg-corrutpion.ll b/test/CodeGen/X86/rrlist-livereg-corrutpion.ll
new file mode 100644
index 00000000000..7191e0453a6
--- /dev/null
+++ b/test/CodeGen/X86/rrlist-livereg-corrutpion.ll
@@ -0,0 +1,26 @@
+; RUN: llc < %s -march=x86-64 | FileCheck %s
+
+; CHECK-LABEL: test
+define i64 @test(i64 %a, i256 %b, i1 %c) {
+  %u = zext i64 %a to i256
+  %s = add i256 %u, 1
+  %o = trunc i256 %s to i1
+  %j = add i256 %s, 1
+  %i = icmp ule i64 %a, 1
+  %f = select i1 %o, i256 undef, i256 %j
+  %d = select i1 %i, i256 %f, i256 1
+  %e = add i256 %b, 1
+  %n = select i1 %c, i256 %e, i256 %b
+  %m = trunc i256 %n to i64
+  %h = add i64 %m, 1
+  %r = zext i64 %h to i256
+  %v = lshr i256 %d, %r
+  %t = trunc i256 %v to i1
+  %q = shl i256 1, %r
+  %p = and i256 %d, %q
+  %w = icmp ule i256 %n, 1
+  %y = select i1 %t, i256 undef, i256 %p
+  %x = select i1 %w, i256 %y, i256 %d
+  %z = trunc i256 %x to i64
+  ret i64 %z
+}