Hi,
The patch changes the default behaviour of the direction in which
the local frame grows for MIPS16.
The code size reduces by about 0.5% in average case for -Os, hence,
it is good to turn the option on by default.
Ok to apply?
Regards,
Robert
gcc/
2016-05-20 Matthew Fortune <matthew.fort...@imgtec.com>
* config/mips/mips.h (FRAME_GROWS_DOWNWARD): Enable it
conditionally for MIPS16.
* config/mips/mips.opt: Add -mgrow-frame-downwards option.
Enable it by default for MIPS16.
* doc/invoke.texi: Document the option.
---
gcc/config/mips/mips.h | 8 +++++++-
gcc/config/mips/mips.opt | 4 ++++
gcc/doc/invoke.texi | 13 +++++++++++++
3 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/gcc/config/mips/mips.h b/gcc/config/mips/mips.h
index 5020208..6ab7dd3 100644
--- a/gcc/config/mips/mips.h
+++ b/gcc/config/mips/mips.h
@@ -2311,7 +2311,13 @@ enum reg_class
#define STACK_GROWS_DOWNWARD 1
-#define FRAME_GROWS_DOWNWARD flag_stack_protect
+/* Growing the frame downwards allows us to put spills closest to
+ the stack pointer which is good as they are likely to be accessed
+ frequently. We can also arrange for normal stack usage to place
+ scalars last so that they too are close to the stack pointer. */
+#define FRAME_GROWS_DOWNWARD ((TARGET_MIPS16 \
+ && TARGET_FRAME_GROWS_DOWNWARDS) \
+ || flag_stack_protect)
/* Size of the area allocated in the frame to save the GP. */
diff --git a/gcc/config/mips/mips.opt b/gcc/config/mips/mips.opt
index 3b92ef5..53feb23 100644
--- a/gcc/config/mips/mips.opt
+++ b/gcc/config/mips/mips.opt
@@ -447,3 +447,7 @@ Enum(mips_cb_setting) String(always) Value(MIPS_CB_ALWAYS)
minline-intermix
Target Report Var(TARGET_INLINE_INTERMIX)
Allow inlining even if the compression flags differ between caller and callee.
+
+mgrow-frame-downwards
+Target Report Var(TARGET_FRAME_GROWS_DOWNWARDS) Init(1)
+Change the behaviour to grow the frame downwards for MIPS16.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 2f6195e..6e5d620 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -838,6 +838,7 @@ Objective-C and Objective-C++ Dialects}.
-minterlink-compressed -mno-interlink-compressed @gol
-minterlink-mips16 -mno-interlink-mips16 @gol
-minline-intermix -mno-inline-intermix @gol
+-mgrow-frame-downwards -mno-grow-frame-downwards @gol
-mabi=@var{abi} -mabicalls -mno-abicalls @gol
-mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol
-mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float @gol
@@ -17929,6 +17930,18 @@ vice-versa. When using this option it is necessary to
protect functions
that cannot be compiled as MIPS16 with a @code{noinline} attribute to ensure
they are not inlined into a MIPS16 function.
+@item -mgrow-frame-downwards
+@itemx -mno-grow-frame-downwards
+@opindex mgrow-frame-downwards
+Grow the local frame down (up) for MIPS16.
+
+Growing the frame downwards allows us to get spill slots created at the lowest
+address rather than the highest address in a local frame. The benefit of this
+is smaller code size as accessing spill splots closer to the stack pointer
+can be done using using 16-bit instructions.
+
+The option is enabled by default (to grow frame downwards) for MIPS16.
+
@item -mabi=32
@itemx -mabi=o64
@itemx -mabi=n32
--
2.8.2.396.g5fe494c
