From: Chad Rosier <mcrosier@codeaurora.org>
Date: Fri, 30 Jan 2015 19:55:40 +0000 (+0000)
Subject: [AArch64] Make AArch64A57FPLoadBalancing output stable.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=cea6171bda84f2396e86e15b460507a739da5d0c;p=oota-llvm.git

[AArch64] Make AArch64A57FPLoadBalancing output stable.

Add tie breaker to colorChainSet() sort so that processing order doesn't
depend on std::set order, which depends on pointer order, which is
unstable from run to run.

No test case as this is nearly impossible to reproduce.

Phabricator Review: http://reviews.llvm.org/D7265
Patch by Geoff Berry <gberry@codeaurora.org>!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227606 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp b/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp
index 1d437614e88..2cf3c2275d6 100644
--- a/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp
+++ b/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp
@@ -272,7 +272,7 @@ public:
   }
 
   /// Return true if this chain starts before Other.
-  bool startsBefore(Chain *Other) {
+  bool startsBefore(const Chain *Other) const {
     return StartInstIdx < Other->StartInstIdx;
   }
 
@@ -442,10 +442,17 @@ bool AArch64A57FPLoadBalancing::colorChainSet(std::vector<Chain*> GV,
   // chains that we cannot change before we look at those we can,
   // so the parity counter is updated and we know what color we should
   // change them to!
+  // Final tie-break with instruction order so pass output is stable (i.e. not
+  // dependent on malloc'd pointer values).
   std::sort(GV.begin(), GV.end(), [](const Chain *G1, const Chain *G2) {
       if (G1->size() != G2->size())
         return G1->size() > G2->size();
-      return G1->requiresFixup() > G2->requiresFixup();
+      if (G1->requiresFixup() != G2->requiresFixup())
+        return G1->requiresFixup() > G2->requiresFixup();
+      // Make sure startsBefore() produces a stable final order.
+      assert((G1 == G2 || (G1->startsBefore(G2) ^ G2->startsBefore(G1))) &&
+             "Starts before not total order!");
+      return G1->startsBefore(G2);
     });
 
   Color PreferredColor = Parity < 0 ? Color::Even : Color::Odd;