RISC-V: Implement C[LT]Z_DEFINED_VALUE_AT_ZERO

The Zbb support has introduced ctz and clz to the backend, but some
transformations in GCC need to know what the value of c[lt]z at zero
is. This affects how the optab is generated and may suppress use of
CLZ/CTZ in tree passes.

Among other things, this is needed for the transformation of
table-based ctz-implementations, such as in deepsjeng, to work
(see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90838).

Prior to this change, the test case from PR90838 would compile to
on RISC-V targets with Zbb:
  myctz:
	lui	a4,%hi(.LC0)
	ld	a4,%lo(.LC0)(a4)
	neg	a5,a0
	and	a5,a5,a0
	mul	a5,a5,a4
	lui	a4,%hi(.LANCHOR0)
	addi	a4,a4,%lo(.LANCHOR0)
	srli	a5,a5,58
	sh2add	a5,a5,a4
	lw	a0,0(a5)
	ret

After this change, we get:
  myctz:
	ctz	a0,a0
	andi	a0,a0,63
	ret

Testing this with deepsjeng_r (from SPEC 2017) against QEMU, this
shows a clear reduction in dynamic instruction count:
 - before  1961888067076
 - after   1907928279874 (2.75% reduction)

This also merges the various target-specific test-cases (for x86-64,
aarch64 and riscv) within gcc.dg/pr90838.c.

This extends the macros (i.e., effective-target keywords) used in
testing (lib/target-supports.exp) to reliably distinguish between RV32
and RV64 via __riscv_xlen (i.e., the integer register bitwidth) :
testing for ILP32 could be misleading (as ILP32 is a valid memory
model for 64bit systems).

gcc/ChangeLog:

	* config/riscv/riscv.h (CLZ_DEFINED_VALUE_AT_ZERO): Implement.
	(CTZ_DEFINED_VALUE_AT_ZERO): Same.
	* doc/sourcebuild.texi: add documentation for RISC-V specific
	test target keywords

gcc/testsuite/ChangeLog:

	* gcc.dg/pr90838.c: Add additional flags (dg-additional-options)
	  when compiling for riscv64 and subsume gcc.target/aarch64/pr90838.c
	  and gcc.target/i386/pr95863-2.c.
	* gcc.target/aarch64/pr90838.c: Removed.
	* gcc.target/i386/pr95863-2.c: Removed.
	* lib/target-supports.exp: Recognize RV32 or RV64 via XLEN

Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
Signed-off-by: Manolis Tsamis <manolis.tsamis@vrull.eu>
Co-authored-by: Manolis Tsamis <manolis.tsamis@vrull.eu>

6 files changed, 72 insertions, 91 deletions

diff --git a/gcc/config/riscv/riscv.h b/gcc/config/riscv/riscv.h
index 8a4d2cf..b191606 100644
--- a/gcc/config/riscv/riscv.h
+++ b/gcc/config/riscv/riscv.h
@@ -1004,4 +1004,9 @@ extern void riscv_remove_unneeded_save_restore_calls (void);
 
 #define HARD_REGNO_RENAME_OK(FROM, TO) riscv_hard_regno_rename_ok (FROM, TO)
 
+#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)
+
 #endif /* ! GCC_RISCV_H */
diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
index 613ac29..71c0484 100644
--- a/gcc/doc/sourcebuild.texi
+++ b/gcc/doc/sourcebuild.texi
@@ -2420,6 +2420,18 @@ PowerPC target pre-defines macro _ARCH_PWR9 which means the @code{-mcpu}
 setting is Power9 or later.
 @end table
 
+@subsection RISC-V specific attributes
+
+@table @code
+
+@item rv32
+Test system has an integer register width of 32 bits.
+
+@item rv64
+Test system has an integer register width of 64 bits.
+
+@end table
+
 @subsubsection Other hardware attributes
 
 @c Please keep this table sorted alphabetically.
diff --git a/gcc/testsuite/gcc.dg/pr90838.c b/gcc/testsuite/gcc.dg/pr90838.c
index 41c5dab..7502b84 100644
--- a/gcc/testsuite/gcc.dg/pr90838.c
+++ b/gcc/testsuite/gcc.dg/pr90838.c
@@ -1,5 +1,8 @@
 /* { dg-do compile } */
 /* { dg-options "-O2 -fdump-tree-forwprop2-details" } */
+/* { dg-additional-options "-mbmi" { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } */
+/* { dg-additional-options "-march=rv64gc_zbb" { target { rv64 } } } */
+/* { dg-additional-options "-march=rv32gc_zbb" { target { rv32 } } } */
 
 int ctz1 (unsigned x)
 {
@@ -56,4 +59,26 @@ int ctz4 (unsigned long x)
   return table[(lsb * magic) >> 58];
 }
 
+/* { dg-final { scan-tree-dump-times {= \.CTZ} 4 "forwprop2" { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
+/* { dg-final { scan-assembler-times "tzcntq\t" 1 { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
+/* { dg-final { scan-assembler-times "tzcntl\t" 3 { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
+/* { dg-final { scan-assembler-times "andl\t" 2 { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
+/* { dg-final { scan-assembler-not "negq" { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
+/* { dg-final { scan-assembler-not "imulq" { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
+/* { dg-final { scan-assembler-not "shrq" { target { { i?86-*-* x86_64-*-* } && { ! { ia32 } } } } } } */
+
 /* { dg-final { scan-tree-dump-times {= \.CTZ} 4 "forwprop2" { target aarch64*-*-* } } } */
+/* { dg-final { scan-assembler-times "clz\t" 4 { target aarch64*-*-* } } } */
+/* { dg-final { scan-assembler-times "and\t" 2 { target aarch64*-*-* } } } */
+/* { dg-final { scan-assembler-not "cmp\t.*0" { target aarch64*-*-* } } } */
+
+/* { dg-final { scan-tree-dump-times {= \.CTZ} 4 "forwprop2" { target { rv64 } } } } */
+/* { dg-final { scan-assembler-times "ctz\t"  1 { target { rv64 } } } } */
+/* { dg-final { scan-assembler-times "ctzw\t" 3 { target { rv64 } } } } */
+/* { dg-final { scan-assembler-times "andi\t" 2 { target { rv64 } } } } */
+/* { dg-final { scan-assembler-not "mul" { target { rv64 } } } } */
+
+/* { dg-final { scan-tree-dump-times {= \.CTZ} 3 "forwprop2" { target { rv32 } } } } */
+/* { 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 } } } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/pr90838.c b/gcc/testsuite/gcc.target/aarch64/pr90838.c
deleted file mode 100644
index e1e19ac..0000000
--- a/gcc/testsuite/gcc.target/aarch64/pr90838.c
+++ /dev/null
@@ -1,64 +0,0 @@
-/* { dg-do compile } */
-/* { dg-options "-O2" } */
-
-int ctz1 (unsigned x)
-{
-  static const char table[32] =
-    {
-      0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
-      31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
-    };
-
-  return table[((unsigned)((x & -x) * 0x077CB531U)) >> 27];
-}
-
-int ctz2 (unsigned x)
-{
-#define u 0
-  static short table[64] =
-    {
-      32, 0, 1,12, 2, 6, u,13, 3, u, 7, u, u, u, u,14,
-      10, 4, u, u, 8, u, u,25, u, u, u, u, u,21,27,15,
-      31,11, 5, u, u, u, u, u, 9, u, u,24, u, u,20,26,
-      30, u, u, u, u,23, u,19,29, u,22,18,28,17,16, u
-    };
-
-  x = (x & -x) * 0x0450FBAF;
-  return table[x >> 26];
-}
-
-int ctz3 (unsigned x)
-{
-  static int table[32] =
-    {
-      0, 1, 2,24, 3,19, 6,25, 22, 4,20,10,16, 7,12,26,
-      31,23,18, 5,21, 9,15,11,30,17, 8,14,29,13,28,27
-    };
-
-  if (x == 0) return 32;
-  x = (x & -x) * 0x04D7651F;
-  return table[x >> 27];
-}
-
-static const unsigned long long magic = 0x03f08c5392f756cdULL;
-
-static const char table[64] = {
-     0,  1, 12,  2, 13, 22, 17,  3,
-    14, 33, 23, 36, 18, 58, 28,  4,
-    62, 15, 34, 26, 24, 48, 50, 37,
-    19, 55, 59, 52, 29, 44, 39,  5,
-    63, 11, 21, 16, 32, 35, 57, 27,
-    61, 25, 47, 49, 54, 51, 43, 38,
-    10, 20, 31, 56, 60, 46, 53, 42,
-     9, 30, 45, 41,  8, 40,  7,  6,
-};
-
-int ctz4 (unsigned long x)
-{
-  unsigned long lsb = x & -x;
-  return table[(lsb * magic) >> 58];
-}
-
-/* { dg-final { scan-assembler-times "clz\t" 4 } } */
-/* { dg-final { scan-assembler-times "and\t" 2 } } */
-/* { dg-final { scan-assembler-not "cmp\t.*0" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr95863-2.c b/gcc/testsuite/gcc.target/i386/pr95863-2.c
deleted file mode 100644
index cb56dfc..0000000
--- a/gcc/testsuite/gcc.target/i386/pr95863-2.c
+++ /dev/null
@@ -1,27 +0,0 @@
-/* { dg-do compile { target { ! ia32 } } } */
-/* { dg-options "-O -mbmi" } */
-
-static const unsigned long long magic = 0x03f08c5392f756cdULL;
-
-static const char table[64] = {
-     0,  1, 12,  2, 13, 22, 17,  3,
-    14, 33, 23, 36, 18, 58, 28,  4,
-    62, 15, 34, 26, 24, 48, 50, 37,
-    19, 55, 59, 52, 29, 44, 39,  5,
-    63, 11, 21, 16, 32, 35, 57, 27,
-    61, 25, 47, 49, 54, 51, 43, 38,
-    10, 20, 31, 56, 60, 46, 53, 42,
-     9, 30, 45, 41,  8, 40,  7,  6,
-};
-
-int ctz4 (unsigned long long x)
-{
-  unsigned long long lsb = x & -x;
-  return table[(lsb * magic) >> 58];
-}
-
-/* { dg-final { scan-assembler-times "tzcntq\t" 1 } } */
-/* { dg-final { scan-assembler-times "andl\t" 1 } } */
-/* { dg-final { scan-assembler-not "negq" } } */
-/* { dg-final { scan-assembler-not "imulq" } } */
-/* { dg-final { scan-assembler-not "shrq" } } */
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 2d5d053..244fe23 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -1689,6 +1689,36 @@ proc check_linker_plugin_available { } {
   } "-flto -fuse-linker-plugin"]
 }
 
+# Return 1 if the target is RV32, 0 otherwise.  Cache the result.
+
+proc check_effective_target_rv32 { } {
+    # Check that we are compiling for RV32 by checking the xlen size.
+    return [check_no_compiler_messages riscv_rv32 assembly {
+       #if !defined(__riscv_xlen)
+       #error "__riscv_xlen not defined!"
+       #else
+       #if __riscv_xlen != 32
+       #error "Not RV32"
+       #endif
+       #endif
+    }]
+}
+
+# Return 1 if the target is RV64, 0 otherwise.  Cache the result.
+
+proc check_effective_target_rv64 { } {
+    # Check that we are compiling for RV64 by checking the xlen size.
+    return [check_no_compiler_messages riscv_rv64 assembly {
+       #if !defined(__riscv_xlen)
+       #error "__riscv_xlen not defined!"
+       #else
+       #if __riscv_xlen != 64
+       #error "Not RV64"
+       #endif
+       #endif
+    }]
+}
+
 # Return 1 if the target OS supports running SSE executables, 0
 # otherwise.  Cache the result.