This fixes a missed optimization in the testcase in PR89698
where we fail to fold an access to a virtual table slot because
it is (int (*) ()) 0 - yes, an unfolded INTEGER_CST. Callers
are not happy with this so the following makes sure to
return a properly folded constant via canonicalize_constructor_val.
This avoids the dynamic_cast<> runtime overhead in the testcase.
Bootstrap & regtest running on x86_64-unknown-linux-gnu, queued for GCC
10.
Richard.
2019-03-14 Richard Biener <rguent...@suse.de>
PR tree-optimization/89698
* gimple-fold.c (canonicalize_constructor_val): Early out
for constants, handle unfolded INTEGER_CSTs as they appear in
C++ virtual table ctors.
* g++.dg/tree-ssa/pr89698.C: New testcase.
Index: gcc/gimple-fold.c
===================================================================
--- gcc/gimple-fold.c (revision 269641)
+++ gcc/gimple-fold.c (working copy)
@@ -207,6 +207,9 @@ create_tmp_reg_or_ssa_name (tree type, g
tree
canonicalize_constructor_val (tree cval, tree from_decl)
{
+ if (CONSTANT_CLASS_P (cval))
+ return cval;
+
tree orig_cval = cval;
STRIP_NOPS (cval);
if (TREE_CODE (cval) == POINTER_PLUS_EXPR
@@ -257,8 +260,15 @@ canonicalize_constructor_val (tree cval,
cval = fold_convert (TREE_TYPE (orig_cval), cval);
return cval;
}
- if (TREE_OVERFLOW_P (cval))
- return drop_tree_overflow (cval);
+ /* In CONSTRUCTORs we may see unfolded constants like (int (*) ()) 0. */
+ if (TREE_CODE (cval) == INTEGER_CST)
+ {
+ if (TREE_OVERFLOW_P (cval))
+ cval = drop_tree_overflow (cval);
+ if (!useless_type_conversion_p (TREE_TYPE (orig_cval), TREE_TYPE (cval)))
+ cval = fold_convert (TREE_TYPE (orig_cval), cval);
+ return cval;
+ }
return orig_cval;
}
Index: gcc/testsuite/g++.dg/tree-ssa/pr89698.C
===================================================================
--- gcc/testsuite/g++.dg/tree-ssa/pr89698.C (nonexistent)
+++ gcc/testsuite/g++.dg/tree-ssa/pr89698.C (working copy)
@@ -0,0 +1,29 @@
+// { dg-do compile }
+// { dg-options "-O -fdump-tree-fre1" }
+
+class A {
+ virtual void f(){};
+public:
+ int x;
+ A(int in): x(in) {};
+};
+
+class B: public A {
+public:
+ int y;
+ B(int in):A(in-1), y(in) {};
+};
+
+void bar(void *);
+void test()
+{
+ B b(2);
+ A* bp = &b;
+ void* vp = dynamic_cast<void*>(bp);
+ bar (vp);
+}
+
+// We should be able to constant fold from the virtual table
+// the offset added to bp for the dynamic cast and forward
+// &b to the argument of bar
+// { dg-final { scan-tree-dump "bar \\\(&b" "fre1" } }
