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[v2] RISCV: Bugfix for wrong code with v16hi compare & mask

Message ID 20230325121432.3203674-1-pan2.li@intel.com
State Accepted
Headers
Series [v2] RISCV: Bugfix for wrong code with v16hi compare & mask |

Checks

Context Check Description
snail/gcc-patch-check success Github commit url

Commit Message

Li, Pan2 via Gcc-patches March 25, 2023, 12:14 p.m. UTC 
  From: yes <pan2.li@intel.com>

Fix the bug of the incorrect code generation for the
below code sample.

typedef unsigned short __attribute__((__vector_size__ (32))) V;
typedef unsigned short u16;

void
foo (V m, u16 *ret)
{
  V v = 6 > ((V) { 2049, 8 } & m);
  *ret = v[0]; // + a + b + c + d;
}

Before this patch.
addi    sp,sp,-64
ld      a5,0(a0)
li      a4,528384
addi    a4,a4,-2047
and     a5,a5,a4
// slli    a5,a5,48 <- eliminated by mistake..
// srli    a5,a5,48 <- eliminated by mistake.
sltiu   a5,a5,6
negw    a5,a5
sh      a5,0(a1)

After this patch.
addi    sp,sp,-64
ld      a5,0(a0)
li      a4,528384
addi    a4,a4,-2047
and     a5,a5,a4
slli    a5,a5,48
srli    a5,a5,48
sltiu   a5,a5,6
negw    a5,a5
sh      a5,0(a1)

The simplify_comparation for the AND operation will
try to simplify below RTL code from:
(and:DI (subreg:DI (reg:HI 154) 0) (const_int 0x801))
to:
(subreg:DI (and (reg:HI 154) (const_int 0x801)) 0)

If reg:HI 154 is 0x801 and reg:DI 154 is 0x80801, the RTL will
be simplified continuely to:
(subreg:DI (reg:HI 154) 0)

That will loss the chance to clean the upper bits of the
reg:DI 154, which result in the slli/srli to be eliminated. This
patch will try 2 times when simplify_gen_binary for both the
reg:HI 154 and the reg:DI 154, and only perform the operation if
the returned simplified RTX equals.

	PR 109040

gcc/ChangeLog:

	* combine.cc (simplify_comparison):

gcc/testsuite/ChangeLog:

	* gcc.dg/pr109040.c: New test.

Signed-off-by: yes <pan2.li@intel.com>
---
 gcc/combine.cc                            | 14 +++++++++++---
 gcc/testsuite/gcc.target/riscv/pr109040.c | 14 ++++++++++++++
 2 files changed, 25 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/riscv/pr109040.c
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Patch

diff --git a/gcc/combine.cc b/gcc/combine.cc
index 053879500b7..7a62c95ddc8 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -12681,10 +12681,18 @@  simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1)
 		  && c1 != mask
 		  && c1 != GET_MODE_MASK (tmode))
 		{
-		  op0 = simplify_gen_binary (AND, tmode,
-					     SUBREG_REG (XEXP (op0, 0)),
+		  rtx op0_exp0 = XEXP (op0, 0);
+		  machine_mode op0_exp0_mode = GET_MODE (op0_exp0);
+		  rtx op0_subreg = simplify_gen_binary (AND, tmode,
+					     SUBREG_REG (op0_exp0),
 					     gen_int_mode (c1, tmode));
-		  op0 = gen_lowpart (mode, op0);
+		  rtx op0_reg = simplify_gen_binary (AND, GET_MODE (op0_exp0),
+					     op0_exp0,
+					     gen_int_mode (c1, op0_exp0_mode));
+		  if (!rtx_equal_p (op0_subreg, op0_reg))
+		    break;
+
+		  op0 = gen_lowpart (mode, op0_reg);
 		  continue;
 		}
 	    }
diff --git a/gcc/testsuite/gcc.target/riscv/pr109040.c b/gcc/testsuite/gcc.target/riscv/pr109040.c
new file mode 100644
index 00000000000..3b72ab319b8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/pr109040.c
@@ -0,0 +1,14 @@ 
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc -mabi=lp64 -O2 -fno-schedule-insns -fno-schedule-insns2" } */
+
+typedef unsigned short __attribute__((__vector_size__ (32))) V;
+typedef unsigned short u16;
+
+void
+foo (V m, u16 *ret)
+{
+  V v = 6 > ((V) { 2049, 8 } & m);
+  *ret = v[0];
+}
+
+/* { dg-final { scan-assembler-times {slli\s+a[0-9]+,\s*a[0-9]+,\s*48\s+srli\s+a[0-9]+,\s*a[0-9]+,\s*48} 1 } } */