Subzero: Allow delaying Phi lowering until after register allocation.

src/IceInst.cpp

Index: src/IceInst.cpp
diff --git a/src/IceInst.cpp b/src/IceInst.cpp
index 4aa6e6947fc030c5c14ba32faa8ee07b21c9b2c0..75360dce95ffaee27a770c17e8c14581f8c36aac 100644
--- a/src/IceInst.cpp
+++ b/src/IceInst.cpp
@@ -135,12 +135,14 @@ void Inst::livenessLightweight(Cfg *Func, LivenessBV &Live) {
   }
 }
 
-void Inst::liveness(InstNumberT InstNumber, LivenessBV &Live,
+// Returns true if the instruction is tentatively retained, or false

[jvoung (off chromium), 2014/10/27 22:12:21]

nit: Might be clearer if the return value is described in terms of live vs dead,
since this is a liveness() function (vs deleted which is what a separate pass
would do with this info)

[Jim Stichnoth, 2014/10/28 01:20:14]

Tried to clarify the description (in the .h file).

+// if the instruction is tentatively deleted.
+bool Inst::liveness(InstNumberT InstNumber, LivenessBV &Live,
                     Liveness *Liveness, LiveBeginEndMap *LiveBegin,
                     LiveBeginEndMap *LiveEnd) {
   assert(!isDeleted());
   if (llvm::isa<InstFakeKill>(this))
-    return;
+    return true;
 
   Dead = false;
   if (Dest) {
@@ -158,7 +160,7 @@ void Inst::liveness(InstNumberT InstNumber, LivenessBV &Live,
     }
   }
   if (Dead)
-    return;
+    return false;
   // Phi arguments only get added to Live in the predecessor node, but
   // we still need to update LiveRangesEnded.
   bool IsPhi = llvm::isa<InstPhi>(this);
@@ -202,6 +204,7 @@ void Inst::liveness(InstNumberT InstNumber, LivenessBV &Live,
       }
     }
   }
+  return true;
 }
 
 InstAlloca::InstAlloca(Cfg *Func, Operand *ByteCount, uint32_t AlignInBytes,
@@ -261,6 +264,17 @@ NodeList InstBr::getTerminatorEdges() const {
   return OutEdges;
 }
 
+bool InstBr::repointEdge(CfgNode *OldNode, CfgNode *NewNode) {
+  if (TargetFalse == OldNode) {
+    TargetFalse = NewNode;
+    return true;
+  } else if (TargetTrue == OldNode) {
+    TargetTrue = NewNode;
+    return true;
+  }
+  return false;

[jvoung (off chromium), 2014/10/27 22:12:21]

Should this always succeed or no (only be one terminator in block)?

[Jim Stichnoth, 2014/10/28 01:20:14]

It should fail (return false) only if something gets out of sync between the
CfgNode edges and the branch instruction.  Note that the caller,
splitIncomingEdge(), asserts that some repointing was successful.

+}
+
 InstCast::InstCast(Cfg *Func, OpKind CastKind, Variable *Dest, Operand *Source)
     : InstHighLevel(Func, Inst::Cast, 1, Dest), CastKind(CastKind) {
   addSource(Source);
@@ -410,6 +424,20 @@ NodeList InstSwitch::getTerminatorEdges() const {
   return OutEdges;
 }
 
+bool InstSwitch::repointEdge(CfgNode *OldNode, CfgNode *NewNode) {
+  if (LabelDefault == OldNode) {
+    LabelDefault = NewNode;
+    return true;
+  }
+  for (SizeT I = 0; I < NumCases; ++I) {
+    if (Labels[I] == OldNode) {
+      Labels[I] = NewNode;
+      return true;
+    }
+  }
+  return false;
+}
+
 InstUnreachable::InstUnreachable(Cfg *Func)
     : InstHighLevel(Func, Inst::Unreachable, 0, NULL) {}