Hi Richard,
here's a new patch, with some quite significant changes to
arm_legitimize_reload_address(). This time fully utilizing the
sign-magnitude offset macro you gave in the last thread, and adapting
your description into embedded comments.
The reload_outdf pattern caused some regressions in a first round of
testing. With the new reload address legitimization, which creates a RTX
like (mem (plus (plus reg #high) #low)), the current
SECONDARY_RELOAD_OUTPUT_CLASS macro returns 'GENERAL_REGS' under VFP,
which triggers the execution of reload_outdf, but now creating
unexpected (set (reg1) (plus (plus reg #high) #low)) insns.
The historical reasons for the reload_outdf pattern are not entirely
clear, as we discussed off list. In any case, we should aim to update
the ARM secondary reload stuff to use the newer framework. I have
disabled the pattern under ARM mode, and cross-tested the entire patch
under v7-A/v5TE VFP, v7-A NEON, and v4T soft-float configs, all clear of
regressions.
reload_outdf is disabled by changing the pattern condition from
TARGET_32BIT to TARGET_THUMB2 (disabling TARGET_ARM only). This is
temporary, Thumb-2 probably needs a few more bits of simultaneous
updates to work, so I'm leaving that for a later patch.
I've listed your name together as significant parts are from you. Is it
ready for trunk?
Thanks,
Chung-Lin
2011-04-08 Chung-Lin Tang <clt...@codesourcery.com>
Richard Earnshaw <rearn...@arm.com>
PR target/48250
* config/arm/arm.c (arm_legitimize_reload_address): Update cases
to use sign-magnitude offsets. Reject unsupported unaligned
cases. Add detailed description in comments.
* config/arm/arm.md (reload_outdf): Disable for ARM mode; change
condition from TARGET_32BIT to TARGET_ARM.
Index: config/arm/arm.c
===================================================================
--- config/arm/arm.c (revision 172057)
+++ config/arm/arm.c (working copy)
@@ -6419,23 +6419,126 @@
HOST_WIDE_INT val = INTVAL (XEXP (*p, 1));
HOST_WIDE_INT low, high;
- if (mode == DImode || (mode == DFmode && TARGET_SOFT_FLOAT))
- low = ((val & 0xf) ^ 0x8) - 0x8;
- else if (TARGET_MAVERICK && TARGET_HARD_FLOAT)
- /* Need to be careful, -256 is not a valid offset. */
- low = val >= 0 ? (val & 0xff) : -((-val) & 0xff);
- else if (mode == SImode
- || (mode == SFmode && TARGET_SOFT_FLOAT)
- || ((mode == HImode || mode == QImode) && ! arm_arch4))
- /* Need to be careful, -4096 is not a valid offset. */
- low = val >= 0 ? (val & 0xfff) : -((-val) & 0xfff);
- else if ((mode == HImode || mode == QImode) && arm_arch4)
- /* Need to be careful, -256 is not a valid offset. */
- low = val >= 0 ? (val & 0xff) : -((-val) & 0xff);
- else if (GET_MODE_CLASS (mode) == MODE_FLOAT
- && TARGET_HARD_FLOAT && TARGET_FPA)
- /* Need to be careful, -1024 is not a valid offset. */
- low = val >= 0 ? (val & 0x3ff) : -((-val) & 0x3ff);
+ /* Detect coprocessor load/stores. */
+ bool coproc_p = ((TARGET_HARD_FLOAT
+ && (TARGET_VFP || TARGET_FPA || TARGET_MAVERICK)
+ && (mode == SFmode || mode == DFmode
+ || (mode == DImode && TARGET_MAVERICK)))
+ || (TARGET_REALLY_IWMMXT
+ && VALID_IWMMXT_REG_MODE (mode))
+ || (TARGET_NEON
+ && (VALID_NEON_DREG_MODE (mode)
+ || VALID_NEON_QREG_MODE (mode))));
+
+ /* For some conditions, bail out when lower two bits are unaligned. */
+ if ((val & 0x3) != 0
+ /* Coprocessor load/store indexes are 8-bits + '00' appended. */
+ && (coproc_p
+ /* For DI, and DF under soft-float: */
+ || ((mode == DImode || mode == DFmode)
+ /* Without ldrd, we use stm/ldm, which does not
+ fair well with unaligned bits. */
+ && (! TARGET_LDRD
+ /* Thumb-2 ldrd/strd is [-1020,+1020] in steps of 4. */
+ || TARGET_THUMB2))))
+ return false;
+
+ /* When breaking down a [reg+index] reload address into [(reg+high)+low],
+ of which the (reg+high) gets turned into a reload add insn,
+ we try to decompose the index into high/low values that can often
+ also lead to better reload CSE.
+ For example:
+ ldr r0, [r2, #4100] // Offset too large
+ ldr r1, [r2, #4104] // Offset too large
+
+ is best reloaded as:
+ add t1, r2, #4096
+ ldr r0, [t1, #4]
+ add t2, r2, #4096
+ ldr r1, [t2, #8]
+
+ which post-reload CSE can simplify in most cases to eliminate the
+ second add instruction:
+ add t1, r2, #4096
+ ldr r0, [t1, #4]
+ ldr r1, [t1, #8]
+
+ The idea here is that we want to split out the bits of the constant
+ as a mask, rather than as subtracting the maximum offset that the
+ respective type of load/store used can handle.
+
+ When encountering negative offsets, we can still utilize it even if
+ the overall offset is positive; sometimes this may lead to an immediate
+ that can be constructed with fewer instructions.
+ For example:
+ ldr r0, [r2, #0x3FFFFC]
+
+ This is best reloaded as:
+ add t1, r2, #0x400000
+ ldr r0, [t1, #-4]
+
+ The trick for spotting this for a load insn with N bits of offset
+ (i.e. bits N-1:0) is to look at bit N; if it is set, then chose a
+ negative offset that is going to make bit N and all the bits below
+ it become zero in the remainder part.
+
+ The SIGN_MAG_LOW_ADDR_BITS macro below implements this, with respect
+ to sign-magnitude addressing (i.e. separate +- bit, or 1's complement),
+ used in most cases of ARM load/store instructions. */
+
+#define SIGN_MAG_LOW_ADDR_BITS(VAL, N) \
+ (((VAL) & ((1 << (N)) - 1)) \
+ ? (((VAL) & ((1 << ((N) + 1)) - 1)) ^ (1 << (N))) - (1 << (N)) \
+ : 0)
+
+ if (coproc_p)
+ low = SIGN_MAG_LOW_ADDR_BITS (val, 10);
+ else if (GET_MODE_SIZE (mode) == 8)
+ {
+ if (TARGET_LDRD)
+ low = (TARGET_THUMB2
+ ? SIGN_MAG_LOW_ADDR_BITS (val, 10)
+ : SIGN_MAG_LOW_ADDR_BITS (val, 8));
+ else
+ /* For pre-ARMv5TE (without ldrd), we use ldm/stm(db/da/ib)
+ to access doublewords. The supported load/store offsets are
+ -8, -4, and 4, which we try to produce here. */
+ low = ((val & 0xf) ^ 0x8) - 0x8;
+ }
+ else if (GET_MODE_SIZE (mode) < 8)
+ {
+ /* NEON element load/stores do not have an offset. */
+ if (TARGET_NEON_FP16 && mode == HFmode)
+ return false;
+
+ if (TARGET_THUMB2)
+ {
+ /* Thumb-2 has an asymmetrical index range of (-256,4096).
+ Try the wider 12-bit range first, and re-try if the result
+ is out of range. */
+ low = SIGN_MAG_LOW_ADDR_BITS (val, 12);
+ if (low < -255)
+ low = SIGN_MAG_LOW_ADDR_BITS (val, 8);
+ }
+ else
+ {
+ if (mode == HImode || mode == HFmode)
+ {
+ if (arm_arch4)
+ low = SIGN_MAG_LOW_ADDR_BITS (val, 8);
+ else
+ {
+ /* The storehi/movhi_bytes fallbacks can use only
+ [-4094,+4094] of the full ldrb/strb index range. */
+ low = SIGN_MAG_LOW_ADDR_BITS (val, 12);
+ if (low == 4095 || low == -4095)
+ return false;
+ }
+ }
+ else
+ low = SIGN_MAG_LOW_ADDR_BITS (val, 12);
+ }
+ }
else
return false;
Index: config/arm/arm.md
===================================================================
--- config/arm/arm.md (revision 172057)
+++ config/arm/arm.md (working copy)
@@ -6188,7 +6188,7 @@
[(match_operand:DF 0 "arm_reload_memory_operand" "=o")
(match_operand:DF 1 "s_register_operand" "r")
(match_operand:SI 2 "s_register_operand" "=&r")]
- "TARGET_32BIT"
+ "TARGET_THUMB2"
"
{
enum rtx_code code = GET_CODE (XEXP (operands[0], 0));
