tcg: Introduce tcg_remove_ops_after

Introduce a function to remove everything emitted
since a given point.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/tcg/tcg.h

@@ -1071,6 +1071,16 @@ void tcg_op_remove(TCGContext *s, TCGOp *op);
 TCGOp *tcg_op_insert_before(TCGContext *s, TCGOp *op, TCGOpcode opc);
 TCGOp *tcg_op_insert_after(TCGContext *s, TCGOp *op, TCGOpcode opc);
 
+/**
+ * tcg_remove_ops_after:
+ * @op: target operation
+ *
+ * Discard any opcodes emitted since @op.  Expected usage is to save
+ * a starting point with tcg_last_op(), speculatively emit opcodes,
+ * then decide whether or not to keep those opcodes after the fact.
+ */
+void tcg_remove_ops_after(TCGOp *op);
+
 void tcg_optimize(TCGContext *s);
 
 /* Allocate a new temporary and initialize it with a constant. */

tcg/tcg.c

@@ -2083,6 +2083,19 @@ void tcg_op_remove(TCGContext *s, TCGOp *op)
 #endif
 }
 
+void tcg_remove_ops_after(TCGOp *op)
+{
+    TCGContext *s = tcg_ctx;
+
+    while (true) {
+        TCGOp *last = tcg_last_op();
+        if (last == op) {
+            return;
+        }
+        tcg_op_remove(s, last);
+    }
+}
+
 static TCGOp *tcg_op_alloc(TCGOpcode opc)
 {
     TCGContext *s = tcg_ctx;