[PATCH] RISC-V: Reset the length to the default of 4 for FP comparisons

["Maciej W. Rozycki" <macro@embecosm.com>]

The default length for floating-point compare operations is overridden 
to 8, however the FEQ.fmt, FLT.fmt, FLE.fmt machine instructions and 
FGE.fmt, FGT.fmt assembly idioms the relevant RTL insns produce are all 
4 bytes long each.  And all the floating-point compare RTL insns that 
produce multiple machine instructions explicitly set their lengths.

Remove the override then, letting the default of 4 apply for the single 
instruction case.

	gcc/
	* config/riscv/riscv.md (length): Remove the explicit setting 
	for "fcmp".
---
Hi,

 So for:

int
feq (float x, float y)
{
  return x == y;
}

we get:

	.globl	feq
	.type	feq, @function
feq:
	feq.s	a0,fa0,fa1	# 15	[c=4 l=8]  *cstoresfdi4
	ret		# 24	[c=0 l=4]  simple_return
	.size	feq, .-feq

which is obviously wrong given:

Disassembly of section .text:

0000000000000000 <feq>:
   0:	a0b52553          	feq.s	a0,fa0,fa1
   4:	8082                	ret

(hmm tabs are odd here too, but that's a binutils issue).  I note that the 
override has always been there since the RISC-V port landed, so I take it 
it's a missed leftover from an earlier situation.

 With the change in place we instead get:

	.globl	feq
	.type	feq, @function
feq:
	feq.s	a0,fa0,fa1	# 15	[c=4 l=4]  *cstoresfdi4
	ret		# 24	[c=0 l=4]  simple_return
	.size	feq, .-feq

which I find so relieving.

 No regressions in the testsuite (and I haven't checked how it affects 
instruction scheduling, especially with `-Os', but I think it's obviously 
correct really).  OK to apply?

  Maciej
---
 gcc/config/riscv/riscv.md |    2 --
 1 file changed, 2 deletions(-)

gcc-riscv-fcmp-length.diff
Index: gcc/gcc/config/riscv/riscv.md
===================================================================
--- gcc.orig/gcc/config/riscv/riscv.md
+++ gcc/gcc/config/riscv/riscv.md
@@ -231,8 +231,6 @@
 
 	  (eq_attr "got" "load") (const_int 8)
 
-	  (eq_attr "type" "fcmp") (const_int 8)
-
 	  ;; SHIFT_SHIFTs are decomposed into two separate instructions.
 	  (eq_attr "move_type" "shift_shift")
 		(const_int 8)