[PATCH] RISC-V: Allow register pairs for 64-bit target.

[Jim Wilson <jimw@sifive.com>]

This was noticed while looking at some 64-bit libgcc code.  Some functions
like negti had a stack frame allocated, but did not use the stack.  The 32-bit
equivalent negdi did not have a stack frame allocated.  This is because a
128-bit local variable got allocated to the stack and then optimized away.
But we allow register pairs for the 32-bit target, we should allow them for
the 64-bit target too.  Fixed by adding a missing definition for
MAX_FIXED_MODE_SIZE.

This was tested by multiple 32-bit and 64-bit newlib and glibc builds and
make checks.  There were no regressions.  The libgcc code for negti no longer
has a stack frame allocated.  libstdc++.so is 3KB smaller with the patch.

Committed.

Jim

	gcc/
	* config/riscv/riscv.h (MAX_FIXED_MODE_SIZE): New.
---
 gcc/config/riscv/riscv.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gcc/config/riscv/riscv.h b/gcc/config/riscv/riscv.h
index a002bff4480..1c1c3431119 100644
--- a/gcc/config/riscv/riscv.h
+++ b/gcc/config/riscv/riscv.h
@@ -158,6 +158,10 @@ along with GCC; see the file COPYING3.  If not see
 
 #define PCC_BITFIELD_TYPE_MATTERS 1
 
+/* An integer expression for the size in bits of the largest integer machine
+   mode that should actually be used.  We allow pairs of registers.  */
+#define MAX_FIXED_MODE_SIZE GET_MODE_BITSIZE (TARGET_64BIT ? TImode : DImode)
+
 /* If defined, a C expression to compute the alignment for a static
    variable.  TYPE is the data type, and ALIGN is the alignment that
    the object would ordinarily have.  The value of this macro is used
-- 
2.14.1