some passing cases, and comments how they work

2 files changed, 55 insertions, 0 deletions

diff --git a/rpython/jit/metainterp/optimizeopt/intbounds.py b/rpython/jit/metainterp/optimizeopt/intbounds.py
index ac09864741..81320b9630 100644
--- a/rpython/jit/metainterp/optimizeopt/intbounds.py
+++ b/rpython/jit/metainterp/optimizeopt/intbounds.py
@@ -305,6 +305,10 @@ class OptIntBounds(Optimization):
             # Transform into INT_ADD.  The following guard will be killed
             # by optimize_GUARD_NO_OVERFLOW; if we see instead an
             # optimize_GUARD_OVERFLOW, then InvalidLoop.
+
+            # NB: this case also takes care of int_add_ovf with 0 as on of the
+            # arguments: the result will be bounded, and then the optimization
+            # for int_add with 0 as argument will remove the op.
             op = self.replace_op_with(op, rop.INT_ADD)
         return self.emit(op)
 
@@ -325,6 +329,7 @@ class OptIntBounds(Optimization):
             return None
         resbound = b0.sub_bound(b1)
         if resbound.bounded():
+            # this case takes care of int_sub_ovf(x, 0) as well
             op = self.replace_op_with(op, rop.INT_SUB)
         return self.emit(op)
 
@@ -342,6 +347,7 @@ class OptIntBounds(Optimization):
         b2 = self.getintbound(op.getarg(1))
         resbound = b1.mul_bound(b2)
         if resbound.bounded():
+            # this case also takes care of multiplication with 0 and 1
             op = self.replace_op_with(op, rop.INT_MUL)
         return self.emit(op)
 
diff --git a/rpython/jit/metainterp/optimizeopt/test/test_optimizebasic.py b/rpython/jit/metainterp/optimizeopt/test/test_optimizebasic.py
index e60c38d652..9b6891eaf5 100644
--- a/rpython/jit/metainterp/optimizeopt/test/test_optimizebasic.py
+++ b/rpython/jit/metainterp/optimizeopt/test/test_optimizebasic.py
@@ -1962,6 +1962,55 @@ class BaseTestOptimizeBasic(BaseTestBasic):
         """
         self.optimize_loop(ops, expected)
 
+        ops = """
+        [i0]
+        i1 = int_mul_ovf(0, i0)
+        guard_no_overflow() []
+        jump(i1)
+        """
+        expected = """
+        [i0]
+        jump(0)
+        """
+        self.optimize_loop(ops, expected)
+
+        ops = """
+        [i0]
+        i1 = int_mul_ovf(i0, 0)
+        guard_no_overflow() []
+        jump(i1)
+        """
+        expected = """
+        [i0]
+        jump(0)
+        """
+        self.optimize_loop(ops, expected)
+
+        ops = """
+        [i0]
+        i1 = int_mul_ovf(1, i0)
+        guard_no_overflow() []
+        jump(i1)
+        """
+        expected = """
+        [i0]
+        jump(i0)
+        """
+        self.optimize_loop(ops, expected)
+
+        ops = """
+        [i0]
+        i1 = int_mul_ovf(i0, 1)
+        guard_no_overflow() []
+        jump(i1)
+        """
+        expected = """
+        [i0]
+        jump(i0)
+        """
+        self.optimize_loop(ops, expected)
+
+
     def test_fold_constant_partial_ops_float(self):
         ops = """
         [f0]