RISC-V: Optimize lui and auipc relaxations for undefweak symbol.

For the lui and auipc relaxations, since the symbol value of an undefined weak
symbol is always be zero, we can optimize the patterns into a single LI/MV/ADDI
instruction.

	bfd/
	* elfnn-riscv.c (riscv_pcgp_hi_reloc): Add new field undefined_weak.
	(riscv_record_pcgp_hi_reloc): New parameter undefined_weak.
	Set undefined_weak field from it.
	(relax_func_t): New parameter undefined_weak.
	(_bfd_riscv_relax_call): New ignored parameter undefined_weak.
	(_bfd_riscv_relax_tls_le): Likewise.
	(_bfd_riscv_relax_align): Likewise.
	(_bfd_riscv_relax_delete): Likewise.
	(_bfd_riscv_relax_lui): New parameter undefined_weak.  If true,
	allow relaxing.  For LO12* relocs, set rs1 to x0 when undefined_weak.
	(_bfd_riscv_relax_pc): New parameter undefined_weak.  For LO12* relocs,
	set undefined_weak from hi_reloc.  If true, allow relaxing.  For LO12*
	relocs, set rs1 to x0 when undefined_weak and change to non-pcrel
	reloc.
	(_bfd_riscv_relax_section): New local undefined_weak.  Set for
	undef weak relocs that can be relaxed.  Pass to relax_func call.

	ld/
	* testsuite/ld-riscv-elf/weakref32.s: Add relaxable undef weak code.
	* testsuite/ld-riscv-elf/weakref64.s: Likewise.
	* testsuite/ld-riscv-elf/weakref32.d: Updated.
	* testsuite/ld-riscv-elf/weakref64.d: Updated.

5 files changed, 39 insertions, 24 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index 3f62dad..57d4df7 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,10 @@
+2019-09-20  Nelson Chu <nelson.chu@sifive.com>
+
+	* testsuite/ld-riscv-elf/weakref32.s: Add relaxable undef weak code.
+	* testsuite/ld-riscv-elf/weakref64.s: Likewise.
+	* testsuite/ld-riscv-elf/weakref32.d: Updated.
+	* testsuite/ld-riscv-elf/weakref64.d: Updated.
+
 2019-09-20  Alan Modra  <amodra@gmail.com>
 
 	* emultempl/xtensaelf.em (xtensa_get_section_deps): Comment.
diff --git a/ld/testsuite/ld-riscv-elf/weakref32.d b/ld/testsuite/ld-riscv-elf/weakref32.d
index 5ede7cb..eaeb6da 100644
--- a/ld/testsuite/ld-riscv-elf/weakref32.d
+++ b/ld/testsuite/ld-riscv-elf/weakref32.d
@@ -5,15 +5,16 @@
 Disassembly of section \.text:
 
 90000000 <_start>:
-90000000:	70000797          	auipc	a5,0x70000
-90000004:	00078793          	mv	a5,a5
-90000008:	02078263          	beqz	a5,9000002c <_start\+0x2c>
-9000000c:	ff010113          	addi	sp,sp,-16
-90000010:	00112623          	sw	ra,12\(sp\)
-90000014:	00000097          	auipc	ra,0x0
-90000018:	000000e7          	jalr	zero # 0 <_start\-0x90000000>
-9000001c:	00c12083          	lw	ra,12\(sp\)
-90000020:	01010113          	addi	sp,sp,16
-90000024:	00000317          	auipc	t1,0x0
-90000028:	00000067          	jr	zero # 0 <_start\-0x90000000>
-9000002c:	00008067          	ret
+90000000:	00000793          	li	a5,0
+90000004:	02078663          	beqz	a5,90000030 <_start\+0x30>
+90000008:	00000793          	li	a5,0
+9000000c:	02078263          	beqz	a5,90000030 <_start\+0x30>
+90000010:	ff010113          	addi	sp,sp,-16
+90000014:	00112623          	sw	ra,12\(sp\)
+90000018:	00000097          	auipc	ra,0x0
+9000001c:	000000e7          	jalr	zero # 0 <_start\-0x90000000>
+90000020:	00c12083          	lw	ra,12\(sp\)
+90000024:	01010113          	addi	sp,sp,16
+90000028:	00000317          	auipc	t1,0x0
+9000002c:	00000067          	jr	zero # 0 <_start\-0x90000000>
+90000030:	00008067          	ret
diff --git a/ld/testsuite/ld-riscv-elf/weakref32.s b/ld/testsuite/ld-riscv-elf/weakref32.s
index 14df041..6c3d84d 100644
--- a/ld/testsuite/ld-riscv-elf/weakref32.s
+++ b/ld/testsuite/ld-riscv-elf/weakref32.s
@@ -4,6 +4,9 @@
 	.globl	_start
 	.type	_start, @function
 _start:
+	lui	a5,%hi(f)
+	addi	a5,a5,%lo(f)
+	beq	a5,zero,.L1
 	lla	a5,f
 	beqz	a5,.L1
 	addi	sp,sp,-16
diff --git a/ld/testsuite/ld-riscv-elf/weakref64.d b/ld/testsuite/ld-riscv-elf/weakref64.d
index 52db9c2..cc718a9 100644
--- a/ld/testsuite/ld-riscv-elf/weakref64.d
+++ b/ld/testsuite/ld-riscv-elf/weakref64.d
@@ -5,15 +5,16 @@
 Disassembly of section \.text:
 
 0000000090000000 <_start>:
-    90000000:	000007b7          	lui	a5,0x0
-    90000004:	00078793          	mv	a5,a5
-    90000008:	02078263          	beqz	a5,9000002c <_start\+0x2c>
-    9000000c:	ff010113          	addi	sp,sp,-16
-    90000010:	00113423          	sd	ra,8\(sp\)
-    90000014:	00000097          	auipc	ra,0x0
-    90000018:	000000e7          	jalr	zero # 0 <_start\-0x90000000>
-    9000001c:	00813083          	ld	ra,8\(sp\)
-    90000020:	01010113          	addi	sp,sp,16
-    90000024:	00000317          	auipc	t1,0x0
-    90000028:	00000067          	jr	zero # 0 <_start\-0x90000000>
-    9000002c:	00008067          	ret
+    90000000:	00000793          	li	a5,0
+    90000004:	02078663          	beqz	a5,90000030 <_start\+0x30>
+    90000008:	00000793          	li	a5,0
+    9000000c:	02078263          	beqz	a5,90000030 <_start\+0x30>
+    90000010:	ff010113          	addi	sp,sp,-16
+    90000014:	00113423          	sd	ra,8\(sp\)
+    90000018:	00000097          	auipc	ra,0x0
+    9000001c:	000000e7          	jalr	zero # 0 <_start\-0x90000000>
+    90000020:	00813083          	ld	ra,8\(sp\)
+    90000024:	01010113          	addi	sp,sp,16
+    90000028:	00000317          	auipc	t1,0x0
+    9000002c:	00000067          	jr	zero # 0 <_start\-0x90000000>
+    90000030:	00008067          	ret
diff --git a/ld/testsuite/ld-riscv-elf/weakref64.s b/ld/testsuite/ld-riscv-elf/weakref64.s
index 5872626..83bcd28 100644
--- a/ld/testsuite/ld-riscv-elf/weakref64.s
+++ b/ld/testsuite/ld-riscv-elf/weakref64.s
@@ -4,6 +4,9 @@
 	.globl	_start
 	.type	_start, @function
 _start:
+	lui	a5,%hi(f)
+	addi	a5,a5,%lo(f)
+	beq	a5,zero,.L1
 	lla	a5,f
 	beqz	a5,.L1
 	addi	sp,sp,-16