Merge "Eliminate debug-moves if their preceding phi-move is sufficient."

3 files changed, 43 insertions, 1 deletions

diff --git a/src/main/java/com/android/tools/r8/ir/code/Value.java b/src/main/java/com/android/tools/r8/ir/code/Value.java
index bf935307f..b6c593c07 100644
--- a/src/main/java/com/android/tools/r8/ir/code/Value.java
+++ b/src/main/java/com/android/tools/r8/ir/code/Value.java
@@ -71,7 +71,7 @@ public class Value {
   private boolean isThis = false;
   private boolean isArgument = false;
   private LongInterval valueRange;
-  private final DebugData debugData;
+  private DebugData debugData;
 
   public Value(int number, MoveType type, DebugInfo debugInfo) {
     this.number = number;
@@ -95,6 +95,12 @@ public class Value {
     return type.requiredRegisters();
   }
 
+  public void setDebugInfo(DebugInfo info) {
+    assert info != null;
+    assert debugData == null;
+    debugData = new DebugData(info);
+  }
+
   public DebugInfo getDebugInfo() {
     return debugData == null ? null : new DebugInfo(debugData.local, debugData.previousLocalValue);
   }
diff --git a/src/main/java/com/android/tools/r8/ir/conversion/IRConverter.java b/src/main/java/com/android/tools/r8/ir/conversion/IRConverter.java
index fad378eaf..a68f29b9b 100644
--- a/src/main/java/com/android/tools/r8/ir/conversion/IRConverter.java
+++ b/src/main/java/com/android/tools/r8/ir/conversion/IRConverter.java
@@ -438,6 +438,10 @@ public class IRConverter {
     printC1VisualizerHeader(method);
     printMethod(code, "Initial IR (SSA)");
 
+    if (options.debug) {
+      codeRewriter.simplifyDebugLocals(code);
+    }
+
     if (!method.isProcessed()) {
       if (protoLiteRewriter != null && protoLiteRewriter.appliesTo(method)) {
         protoLiteRewriter.rewriteProtoLiteSpecialMethod(code, method);
diff --git a/src/main/java/com/android/tools/r8/ir/optimize/CodeRewriter.java b/src/main/java/com/android/tools/r8/ir/optimize/CodeRewriter.java
index 78d8369e3..b4aaa86eb 100644
--- a/src/main/java/com/android/tools/r8/ir/optimize/CodeRewriter.java
+++ b/src/main/java/com/android/tools/r8/ir/optimize/CodeRewriter.java
@@ -37,6 +37,7 @@ import com.android.tools.r8.ir.code.Cmp.Bias;
 import com.android.tools.r8.ir.code.ConstInstruction;
 import com.android.tools.r8.ir.code.ConstNumber;
 import com.android.tools.r8.ir.code.ConstString;
+import com.android.tools.r8.ir.code.DebugLocalWrite;
 import com.android.tools.r8.ir.code.DominatorTree;
 import com.android.tools.r8.ir.code.Goto;
 import com.android.tools.r8.ir.code.IRCode;
@@ -1146,6 +1147,37 @@ public class CodeRewriter {
     }
   }
 
+  public void simplifyDebugLocals(IRCode code) {
+    for (BasicBlock block : code.blocks) {
+      for (Phi phi : block.getPhis()) {
+        if (phi.getDebugInfo() == null && phi.numberOfUsers() == 1 && phi.numberOfAllUsers() == 1) {
+          Instruction instruction = phi.uniqueUsers().iterator().next();
+          if (instruction.isDebugLocalWrite()) {
+            removeDebugWriteOfPhi(phi, instruction.asDebugLocalWrite());
+          }
+        }
+      }
+    }
+  }
+
+  private void removeDebugWriteOfPhi(Phi phi, DebugLocalWrite write) {
+    assert write.src() == phi;
+    Value previousLocalValue = write.getPreviousLocalValue();
+    if (previousLocalValue != null) {
+      if (phi.getOperands().contains(previousLocalValue)) {
+        // The phi is explicitly redefining the local already.
+        previousLocalValue.removeDebugUser(write);
+      } else {
+        // If the phi would redefine a local the debug-write instruction must remain.
+        return;
+      }
+    }
+    phi.setDebugInfo(write.getDebugInfo());
+    phi.removeUser(write);
+    write.outValue().replaceUsers(phi);
+    write.getBlock().removeInstruction(write);
+  }
+
   private static class ExpressionEquivalence extends Equivalence<Instruction> {
 
     @Override