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[RFC,6/8] RISC-V: Use li and rori to load constants.

Message ID 20210923075731.50125-7-kito.cheng@sifive.com
State Committed
Commit 26d2818bb73a09622f87df53d6280d18b229bcbc
Headers show
Series RISC-V: Bit-manipulation extension. | expand

Commit Message

Kito Cheng Sept. 23, 2021, 7:57 a.m. UTC
From: Jim Wilson <jimw@sifive.com>

gcc/ChangeLog:

	* config/riscv/riscv.c (riscv_build_integer_1): Build integer
	with rotate.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/zbb-li-rotr.c: New.
---
 gcc/config/riscv/riscv.c                     | 41 ++++++++++++++++++++
 gcc/testsuite/gcc.target/riscv/zbb-li-rotr.c | 35 +++++++++++++++++
 2 files changed, 76 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/riscv/zbb-li-rotr.c
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Patch

diff --git a/gcc/config/riscv/riscv.c b/gcc/config/riscv/riscv.c
index 10f7bd21f8d..66daebbbc8f 100644
--- a/gcc/config/riscv/riscv.c
+++ b/gcc/config/riscv/riscv.c
@@ -461,6 +461,47 @@  riscv_build_integer_1 (struct riscv_integer_op codes[RISCV_MAX_INTEGER_OPS],
 	}
     }
 
+  if (cost > 2 && TARGET_64BIT && TARGET_ZBB)
+    {
+      int leading_ones = clz_hwi (~value);
+      int trailing_ones = ctz_hwi (~value);
+
+      /* If all bits are one except a few that are zero, and the zero bits
+	 are within a range of 11 bits, and at least one of the upper 32-bits
+	 is a zero, then we can generate a constant by loading a small
+	 negative constant and rotating.  */
+      if (leading_ones < 32
+	  && ((64 - leading_ones - trailing_ones) < 12))
+	{
+	  codes[0].code = UNKNOWN;
+	  /* The sign-bit might be zero, so just rotate to be safe.  */
+	  codes[0].value = (((unsigned HOST_WIDE_INT) value >> trailing_ones)
+			    | (value << (64 - trailing_ones)));
+	  codes[1].code = ROTATERT;
+	  codes[1].value = 64 - trailing_ones;
+	  cost = 2;
+	}
+      /* Handle the case where the 11 bit range of zero bits wraps around.  */
+      else
+	{
+	  int upper_trailing_ones = ctz_hwi (~value >> 32);
+	  int lower_leading_ones = clz_hwi (~value << 32);
+
+	  if (upper_trailing_ones < 32 && lower_leading_ones < 32
+	      && ((64 - upper_trailing_ones - lower_leading_ones) < 12))
+	    {
+	      codes[0].code = UNKNOWN;
+	      /* The sign-bit might be zero, so just rotate to be safe.  */
+	      codes[0].value = ((value << (32 - upper_trailing_ones))
+				| ((unsigned HOST_WIDE_INT) value
+				   >> (32 + upper_trailing_ones)));
+	      codes[1].code = ROTATERT;
+	      codes[1].value = 32 - upper_trailing_ones;
+	      cost = 2;
+	    }
+	}
+    }
+
   gcc_assert (cost <= RISCV_MAX_INTEGER_OPS);
   return cost;
 }
diff --git a/gcc/testsuite/gcc.target/riscv/zbb-li-rotr.c b/gcc/testsuite/gcc.target/riscv/zbb-li-rotr.c
new file mode 100644
index 00000000000..03254ed9150
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zbb-li-rotr.c
@@ -0,0 +1,35 @@ 
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc_zbb -mabi=lp64 -O2" } */
+
+long
+li_rori (void)
+{
+  return 0xffff77ffffffffffL;
+}
+
+long
+li_rori_2 (void)
+{
+  return 0x77ffffffffffffffL;
+}
+
+long
+li_rori_3 (void)
+{
+  return 0xfffffffeefffffffL;
+}
+
+long
+li_rori_4 (void)
+{
+  return 0x5ffffffffffffff5L;
+}
+
+long
+li_rori_5 (void)
+{
+  return 0xaffffffffffffffaL;
+}
+
+
+/* { dg-final { scan-assembler-times "rori\t" 5 } } */