[PATCH, gcc-7] Fix riscv linux kernel boot failure.

[Jim Wilson]

This patch is necessary in order to successfully boot a linux kernel on the
UCB spike simulator.

Riscv loads sign-extend by default, but this wasn't explicitly mentioned in
the pic load patterns, resulting in some bad code generation.  Fixed by adding
an explicit sign_extend operation to the current pattern, and adding a second
pattern for the zero_extend case.

Tested with a linux kernel boot on spike, and a gcc testsuite run.  There were
no regressions.

Committed.

	gcc/
	Backport from mainline
	2017-10-25  Palmer Dabbelt  <palmer@dabbelt.com>

	* config/riscv/riscv.md (ZERO_EXTEND_LOAD): Define.
	* config/riscv/pic.md (local_pic_load): Rename to local_pic_load_s,
	mark as a sign-extending load.
	(local_pic_load_u): Define.
---
 gcc/config/riscv/pic.md   | 11 +++++++++--
 gcc/config/riscv/riscv.md |  3 +++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/gcc/config/riscv/pic.md b/gcc/config/riscv/pic.md
index 6a29ead..03b8f9b 100644
--- a/gcc/config/riscv/pic.md
+++ b/gcc/config/riscv/pic.md
@@ -22,13 +22,20 @@
 ;; Simplify PIC loads to static variables.
 ;; These should go away once we figure out how to emit auipc discretely.
 
-(define_insn "*local_pic_load<mode>"
+(define_insn "*local_pic_load_s<mode>"
   [(set (match_operand:ANYI 0 "register_operand" "=r")
-	(mem:ANYI (match_operand 1 "absolute_symbolic_operand" "")))]
+	(sign_extend:ANYI (mem:ANYI (match_operand 1 "absolute_symbolic_operand" ""))))]
   "USE_LOAD_ADDRESS_MACRO (operands[1])"
   "<load>\t%0,%1"
   [(set (attr "length") (const_int 8))])
 
+(define_insn "*local_pic_load_u<mode>"
+  [(set (match_operand:ZERO_EXTEND_LOAD 0 "register_operand" "=r")
+	(zero_extend:ZERO_EXTEND_LOAD (mem:ZERO_EXTEND_LOAD (match_operand 1 "absolute_symbolic_operand" ""))))]
+  "USE_LOAD_ADDRESS_MACRO (operands[1])"
+  "<load>u\t%0,%1"
+  [(set (attr "length") (const_int 8))])
+
 (define_insn "*local_pic_load<mode>"
   [(set (match_operand:ANYF 0 "register_operand" "=f")
 	(mem:ANYF (match_operand 1 "absolute_symbolic_operand" "")))
diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md
index 4cbb243..c478e03 100644
--- a/gcc/config/riscv/riscv.md
+++ b/gcc/config/riscv/riscv.md
@@ -259,6 +259,9 @@
 ;; Iterator for QImode extension patterns.
 (define_mode_iterator SUPERQI [HI SI (DI "TARGET_64BIT")])
 
+;; Iterator for extending loads.
+(define_mode_iterator ZERO_EXTEND_LOAD [QI HI (SI "TARGET_64BIT")])
+
 ;; Iterator for hardware integer modes narrower than XLEN.
 (define_mode_iterator SUBX [QI HI (SI "TARGET_64BIT")])
 
-- 
2.7.4