[llvm] r227606 - [AArch64] Make AArch64A57FPLoadBalancing output stable.

[Chad Rosier]

Author: mcrosier
Date: Fri Jan 30 13:55:40 2015
New Revision: 227606

URL: http://llvm.org/viewvc/llvm-project?rev=227606&view=rev
Log:
[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 at codeaurora.org>!

Modified:
    llvm/trunk/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp

Modified: llvm/trunk/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp?rev=227606&r1=227605&r2=227606&view=diff
==============================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp (original)
+++ llvm/trunk/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp Fri Jan 30 13:55:40 2015
@@ -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::colorCha
   // 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;