Disable break optimization and change return check to use full mask.

stmt.cpp

@@ -447,6 +447,8 @@ IfStmt::EmitCode(FunctionEmitContext *ctx) const {
         ctx->SetCurrentBasicBlock(bexit);
         ctx->EndIf();
     }
+    /*
+    // Disabled for performance reasons.  Change to an optional compile-time opt switch.
     else if (lCanApplyBreakOptimization(trueStmts, falseStmts)) {
         // If we have a simple break statement inside the 'if' and are
         // under varying control flow, just update the execution mask
@@ -456,6 +458,7 @@ IfStmt::EmitCode(FunctionEmitContext *ctx) const {
         // benefit in this case.
         ctx->SetInternalMaskAndNot(ctx->GetInternalMask(), testValue);
     }
+    */
     else
         emitVaryingIf(ctx, testValue);
 }