aarch64: Improve cost of `a ? {-,}1 : b`

Message ID 20231127230845.615689-1-quic_apinski@quicinc.com
State Committed
Commit d29d27bde5df89e5357e0a33a71bb49125bd1655
Headers
Series aarch64: Improve cost of `a ? {-,}1 : b` |

Checks

Context Check Description
linaro-tcwg-bot/tcwg_gcc_build--master-arm warning Patch is already merged
linaro-tcwg-bot/tcwg_gcc_build--master-aarch64 warning Patch is already merged

Commit Message

Andrew Pinski (QUIC) Nov. 27, 2023, 11:08 p.m. UTC
  While looking into PR 112454, I found the cost for
`(if_then_else (cmp) (const_int 1) (reg))` was being recorded as 8
(or `COSTS_N_INSNS (2)`) but it should have been 4 (or `COSTS_N_INSNS (1)`).
This improves the cost by not adding the cost of `(const_int 1)` to
the total cost.

It does not does not fully fix PR 112454 as that requires other changes to forwprop
the `(const_int 1)` earlier than combine. Though we do fix the loop case where the
constant was only used once.

Committed as approved after bootstrapped and tested on aarch64-linux-gnu with no regressions.

gcc/ChangeLog:

	* config/aarch64/aarch64.cc (aarch64_if_then_else_costs):
	Handle csinv/csinc case of 1/-1.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/csinc-3.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>
---
 gcc/config/aarch64/aarch64.cc              | 12 ++++++++++++
 gcc/testsuite/gcc.target/aarch64/csinc-3.c | 10 ++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/aarch64/csinc-3.c
  

Patch

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index b2093430937..4fd8c2de43a 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -11607,6 +11607,18 @@  aarch64_if_then_else_costs (rtx op0, rtx op1, rtx op2, int *cost, bool speed)
 	    /* CSINV/NEG with zero extend + const 0 (*csinv3_uxtw_insn3).  */
 	    op1 = XEXP (inner, 0);
 	}
+      else if (op1 == constm1_rtx || op1 == const1_rtx)
+	{
+	  /* Use CSINV or CSINC.  */
+	  *cost += rtx_cost (op2, VOIDmode, IF_THEN_ELSE, 2, speed);
+	  return true;
+	}
+      else if (op2 == constm1_rtx || op2 == const1_rtx)
+	{
+	  /* Use CSINV or CSINC.  */
+	  *cost += rtx_cost (op1, VOIDmode, IF_THEN_ELSE, 1, speed);
+	  return true;
+	}
 
       *cost += rtx_cost (op1, VOIDmode, IF_THEN_ELSE, 1, speed);
       *cost += rtx_cost (op2, VOIDmode, IF_THEN_ELSE, 2, speed);
diff --git a/gcc/testsuite/gcc.target/aarch64/csinc-3.c b/gcc/testsuite/gcc.target/aarch64/csinc-3.c
new file mode 100644
index 00000000000..bde131a584e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/csinc-3.c
@@ -0,0 +1,10 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-tree-vectorize" } */
+
+int f(int *a, int n, int *b, int d)
+{
+  for(int i = 0; i < n; i++)
+    b[i] = a[i] == 100 ? 1 : d;
+  /* { dg-final { scan-assembler "csinc\tw\[0-9\].*wzr" } } */
+  return 0;
+}