On Thu, 9 Feb 2017, Richard Biener wrote:
>
> The following patch fixes a missed optimization caused by niter analysis
> returning a complex pointer subtraction expression instead of a constant
> for a loop with a pointer IV (it looks like pointer IVs are quite common
> in libstdc++).
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>
> Not a regression (well, didn't try to find a release where we optimized
> the testcase, but it needs c++14 library support anyway). I'm also
> not quite sure associate_trees handles pointer types correctly
> (there is some pointer type handling in the associate case but
> POINTER_PLUS_EXPR folding for example does not dispatch to associate).
>
> I guess trying to add some more exhaustive testcases for GENERIC input
> is required.
I've generalized a bit and convinced myself it is safe.
Bootstrapped and tested on x86_64-unknow-linux-gnu, applied to trunk.
Richard.
2017-04-21 Richard Biener <rguent...@suse.de>
PR tree-optimization/78847
* fold-const.c (split_tree): Handle POINTER_PLUS_EXPR.
* g++.dg/tree-ssa/pr78847.C: New testcase.
Index: gcc/testsuite/g++.dg/tree-ssa/pr78847.C
===================================================================
*** gcc/testsuite/g++.dg/tree-ssa/pr78847.C (nonexistent)
--- gcc/testsuite/g++.dg/tree-ssa/pr78847.C (working copy)
***************
*** 0 ****
--- 1,26 ----
+ /* { dg-do compile } */
+ /* { dg-require-effective-target c++14 } */
+ /* { dg-options "-O3 -fdump-tree-ldist" } */
+
+ #include <stddef.h>
+ #include <cstring>
+ #include <experimental/string_view>
+
+ using string_view = std::experimental::string_view;
+
+ class Foo {
+ constexpr static size_t Length = 9;
+ char ascii_[Length];
+ public:
+ Foo();
+ string_view view() const {
+ return string_view(ascii_, Length);
+ }
+ };
+
+ void testWithLoopValue(const Foo foo, size_t ptr, char *buf_) {
+ for (auto c : foo.view())
+ buf_[ptr++] = c;
+ }
+
+ /* { dg-final { scan-tree-dump "memcpy\[^\n\r\]*, 9\\);" "ldist" } } */
Index: gcc/fold-const.c
===================================================================
--- gcc/fold-const.c (revision 247049)
+++ gcc/fold-const.c (working copy)
@@ -798,8 +798,11 @@ split_tree (location_t loc, tree in, tre
though the C standard doesn't say so) for integers because
the value is not affected. For reals, the value might be
affected, so we can't. */
- && ((code == PLUS_EXPR && TREE_CODE (in) == MINUS_EXPR)
- || (code == MINUS_EXPR && TREE_CODE (in) == PLUS_EXPR))))
+ && ((code == PLUS_EXPR && TREE_CODE (in) == POINTER_PLUS_EXPR)
+ || (code == PLUS_EXPR && TREE_CODE (in) == MINUS_EXPR)
+ || (code == MINUS_EXPR
+ && (TREE_CODE (in) == PLUS_EXPR
+ || TREE_CODE (in) == POINTER_PLUS_EXPR)))))
{
tree op0 = TREE_OPERAND (in, 0);
tree op1 = TREE_OPERAND (in, 1);
