[gcc r14-5547] LoongArch: Implement C[LT]Z_DEFINED_VALUE_AT_ZERO

[LuluCheng <chenglulu@gcc.gnu.org>]

https://gcc.gnu.org/g:5c8cb429762062f851a56801f021d81f4ecfe3d9

commit r14-5547-g5c8cb429762062f851a56801f021d81f4ecfe3d9
Author: Li Wei <liwei@loongson.cn>
Date:   Fri Nov 17 10:38:02 2023 +0800

    LoongArch: Implement C[LT]Z_DEFINED_VALUE_AT_ZERO
    
    The LoongArch has defined ctz and clz on the backend, but if we want GCC
    do CTZ transformation optimization in forwprop2 pass, GCC need to know
    the value of c[lt]z at zero, which may be beneficial for some test cases
    (like spec2017 deepsjeng_r).
    
    After implementing the macro, we test dynamic instruction count on
    deepsjeng_r:
    - before 1688423249186
    - after  1660311215745 (1.66% reduction)
    
    gcc/ChangeLog:
    
            * config/loongarch/loongarch.h (CLZ_DEFINED_VALUE_AT_ZERO):
            Implement.
            (CTZ_DEFINED_VALUE_AT_ZERO): Same.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/pr90838.c: add clz/ctz test support on LoongArch.

Diff:
---
 gcc/config/loongarch/loongarch.h | 5 +++++
 gcc/testsuite/gcc.dg/pr90838.c   | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/gcc/config/loongarch/loongarch.h b/gcc/config/loongarch/loongarch.h
index ddac8e98ea9..115222e70fd 100644
--- a/gcc/config/loongarch/loongarch.h
+++ b/gcc/config/loongarch/loongarch.h
@@ -1239,3 +1239,8 @@ struct GTY (()) machine_function
 
 #define TARGET_EXPLICIT_RELOCS \
   (la_opt_explicit_relocs == EXPLICIT_RELOCS_ALWAYS)
+
+#define CLZ_DEFINED_VALUE_AT_ZERO(MODE, VALUE) \
+  ((VALUE) = GET_MODE_UNIT_BITSIZE (MODE), 2)
+#define CTZ_DEFINED_VALUE_AT_ZERO(MODE, VALUE) \
+  ((VALUE) = GET_MODE_UNIT_BITSIZE (MODE), 2)
diff --git a/gcc/testsuite/gcc.dg/pr90838.c b/gcc/testsuite/gcc.dg/pr90838.c
index 759059683a9..40aad70499d 100644
--- a/gcc/testsuite/gcc.dg/pr90838.c
+++ b/gcc/testsuite/gcc.dg/pr90838.c
@@ -83,3 +83,8 @@ int ctz4 (unsigned long x)
 /* { dg-final { scan-assembler-times "ctz\t" 3 { target { rv32 } } } } */
 /* { dg-final { scan-assembler-times "andi\t" 1 { target { rv32 } } } } */
 /* { dg-final { scan-assembler-times "mul\t" 1 { target { rv32 } } } } */
+
+/* { dg-final { scan-tree-dump-times {= \.CTZ} 4 "forwprop2" { target { loongarch64*-*-* } } } } */
+/* { dg-final { scan-assembler-times "ctz.d\t" 1 { target { loongarch64*-*-* } } } } */
+/* { dg-final { scan-assembler-times "ctz.w\t" 3 { target { loongarch64*-*-* } } } } */
+/* { dg-final { scan-assembler-times "andi\t" 4 { target { loongarch64*-*-* } } } } */