Fix PR3149. If an early clobber def is a physical register and it is tied to an input operand, it effectively extends the live range of the physical register. Currently we do not have a good way to represent this.

172     %ECX<def> = MOV32rr %reg1039<kill>
180     INLINEASM <es:subl $5,$1
        sbbl $3,$0>, 10, %EAX<def>, 14, %ECX<earlyclobber,def>, 9, %EAX<kill>,
36, <fi#0>, 1, %reg0, 0, 9, %ECX<kill>, 36, <fi#1>, 1, %reg0, 0
188     %EAX<def> = MOV32rr %EAX<kill>
196     %ECX<def> = MOV32rr %ECX<kill>
204     %ECX<def> = MOV32rr %ECX<kill>
212     %EAX<def> = MOV32rr %EAX<kill>
220     %EAX<def> = MOV32rr %EAX
228     %reg1039<def> = MOV32rr %ECX<kill>

The early clobber operand ties ECX input to the ECX def.

The live interval of ECX is represented as this:
%reg20,inf = [46,47:1)[174,230:0)  0@174-(230) 1@46-(47)

The right way to represent this is something like
%reg20,inf = [46,47:2)[174,182:1)[181:230:0)  0@174-(182) 1@181-230 @2@46-(47)

Of course that won't work since that means overlapping live ranges defined by two val#.

The workaround for now is to add a bit to val# which says the val# is redefined by a early clobber def somewhere. This prevents the move at 228 from being optimized away by SimpleRegisterCoalescing::AdjustCopiesBackFrom.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61259 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 3 deletions

diff --git a/include/llvm/CodeGen/LiveInterval.h b/include/llvm/CodeGen/LiveInterval.h
index 7ef2489..4062480 100644
--- a/include/llvm/CodeGen/LiveInterval.h
+++ b/include/llvm/CodeGen/LiveInterval.h
@@ -38,16 +38,19 @@ namespace llvm {
   ///         - or reg # of the definition if it's a stack slot liveinterval.
   ///   copy  - Copy iff val# is defined by a copy; zero otherwise.
   ///   hasPHIKill - One or more of the kills are PHI nodes.
+  ///   redefByEC - Re-defined by early clobber somewhere during the live range.
   ///   kills - Instruction # of the kills.
   struct VNInfo {
     unsigned id;
     unsigned def;
     MachineInstr *copy;
-    bool hasPHIKill;
+    bool hasPHIKill : 1;
+    bool redefByEC : 1;
     SmallVector<unsigned, 4> kills;
-    VNInfo() : id(~1U), def(~1U), copy(0), hasPHIKill(false) {}
+    VNInfo()
+      : id(~1U), def(~1U), copy(0), hasPHIKill(false), redefByEC(false) {}
     VNInfo(unsigned i, unsigned d, MachineInstr *c)
-      : id(i), def(d), copy(c), hasPHIKill(false) {}
+      : id(i), def(d), copy(c), hasPHIKill(false), redefByEC(false) {}
   };
 
   /// LiveRange structure - This represents a simple register range in the
@@ -177,6 +180,7 @@ namespace llvm {
       DstValNo->def = SrcValNo->def;
       DstValNo->copy = SrcValNo->copy;
       DstValNo->hasPHIKill = SrcValNo->hasPHIKill;
+      DstValNo->redefByEC = SrcValNo->redefByEC;
       DstValNo->kills = SrcValNo->kills;
     }