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[PATCH] Fix PR46932: Block auto increment on frame pointer
- From: Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Cc: nd <nd at arm dot com>
- Date: Thu, 20 Jul 2017 14:49:10 +0000
- Subject: [PATCH] Fix PR46932: Block auto increment on frame pointer
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Block auto increment on frame pointer references. This is never
beneficial since the SFP expands into SP+C or FP+C during register
allocation. The generated code for the testcase is now as expected:
str x30, [sp, -32]!
strb w0, [sp, 31]
add x0, sp, 31
bl foo3
ldr x30, [sp], 32
ret
On SPEC2017 codesize improves uniformly across the board.
ChangeLog:
2017-07-20 Wilco Dijkstra <wdijkstr@arm.com>
PR middle-end/46932
* auto-inc-dec.c (parse_add_or_inc): Block autoinc on sfp.
gcc/testsuite/
* gcc.dg/pr46932.c: New testcase.
--
diff --git a/gcc/auto-inc-dec.c b/gcc/auto-inc-dec.c
index 91fa5cf0bbe04b8a2c2c2b9209d245a327de0ffd..db1bd5bba2cee9fbf24d6d522505ac292688aab9 100644
--- a/gcc/auto-inc-dec.c
+++ b/gcc/auto-inc-dec.c
@@ -769,6 +769,12 @@ parse_add_or_inc (rtx_insn *insn, bool before_mem)
inc_insn.pat = pat;
inc_insn.reg_res = SET_DEST (pat);
inc_insn.reg0 = XEXP (SET_SRC (pat), 0);
+
+ /* Block any auto increment of the frame pointer since it expands into
+ an addition and cannot be removed by copy propagation. */
+ if (inc_insn.reg0 == frame_pointer_rtx)
+ return false;
+
if (rtx_equal_p (inc_insn.reg_res, inc_insn.reg0))
inc_insn.form = before_mem ? FORM_PRE_INC : FORM_POST_INC;
else
diff --git a/gcc/testsuite/gcc.dg/pr46932.c b/gcc/testsuite/gcc.dg/pr46932.c
new file mode 100644
index 0000000000000000000000000000000000000000..b96febcc095fbec2cc4e02d1155871220d17cc99
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr46932.c
@@ -0,0 +1,13 @@
+/* { dg-options "-O2 -fdump-rtl-auto_inc_dec" } */
+
+/* Check that accesses based on the frame pointer do not
+ use auto increment. */
+
+extern void foo (char*);
+void t01 (char t)
+{
+ char c = t;
+ foo (&c);
+}
+
+/* { dg-final { scan-rtl-dump-not "success" "auto_inc_dec" } } */