simplify-rtx: Handle `a != 0 ? -a : 0` [PR58195]

The gimple (and generic) levels have this optmization since r12-2041-g7d6979197274a662da7bdc5.
It seems like a good idea to add a similar one to rtl just in case it is not caught at the
gimple level.

Note the loop case in csel-neg-1.c is not handled at the gimple level (even with phiopt turned back on),
this is because of casts to avoid signed integer overflow; a patch to fix this at the gimple level will be
submitted seperately.

Changes since v1:
* v2: Use `CONST0_RTX (mode)` instead of const0_rtx. Add csel-neg-2.c for float testcase which now passes.

Build and tested for aarch64-linux-gnu.

	PR rtl-optimization/58195

gcc/ChangeLog:

	* simplify-rtx.cc (simplify_context::simplify_ternary_operation): Handle
	`a != 0 ? -a : 0` and `a == 0 ? 0 : -a`.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/csel-neg-1.c: New test.
	* gcc.target/aarch64/csel-neg-2.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
index e9591680f7c97afaf45b063c41d09eecdf44159f..2c04ce960ee4953fdddd39f32207031c37a5f1c0 100644 (file)
--- a/gcc/simplify-rtx.cc
+++ b/gcc/simplify-rtx.cc
@@ -6909,6 +6909,28 @@ simplify_context::simplify_ternary_operation (rtx_code code, machine_mode mode,
                  && rtx_equal_p (XEXP (op0, 1), op1))))
        return op2;
 
+      /* Convert a != 0 ? -a : 0 into "-a".  */
+      if (GET_CODE (op0) == NE
+         && ! side_effects_p (op0)
+         && ! HONOR_NANS (mode)
+         && ! HONOR_SIGNED_ZEROS (mode)
+         && XEXP (op0, 1) == CONST0_RTX (mode)
+         && op2 == CONST0_RTX (mode)
+         && GET_CODE (op1) == NEG
+         && rtx_equal_p (XEXP (op0, 0), XEXP (op1, 0)))
+       return op1;
+
+      /* Convert a == 0 ? 0 : -a into "-a".  */
+      if (GET_CODE (op0) == EQ
+         && ! side_effects_p (op0)
+         && ! HONOR_NANS (mode)
+         && ! HONOR_SIGNED_ZEROS (mode)
+         && op1 == CONST0_RTX (mode)
+         && XEXP (op0, 1) == CONST0_RTX (mode)
+         && GET_CODE (op2) == NEG
+         && rtx_equal_p (XEXP (op0, 0), XEXP (op2, 0)))
+       return op2;
+
       /* Convert (!c) != {0,...,0} ? a : b into
          c != {0,...,0} ? b : a for vector modes.  */
       if (VECTOR_MODE_P (GET_MODE (op1))

diff --git a/gcc/testsuite/gcc.target/aarch64/csel-neg-1.c b/gcc/testsuite/gcc.target/aarch64/csel-neg-1.c
new file mode 100644 (file)
index 0000000..7551965
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/csel-neg-1.c
@@ -0,0 +1,31 @@
+/* { dg-do compile } */
+/* Disable phiopt as that will optimize away the `?:`,
+   want to test simplify-rtx */
+/* { dg-options "-O2 -fno-ssa-phiopt" } */
+
+/* PR rtl-optimization/58195 */
+
+int a2(int input)
+{
+  if (input == 0)
+    return 0;
+  return -input;
+}
+int a1(int input)
+{
+    int t = -input;
+    return input == 0 ? 0 : t;
+}
+
+int a(int input)
+{
+    int value = 0;
+    for(int n = input; n != 0; ++n)
+        ++value;
+    return value;
+}
+
+/* There should be no comparison against 0 here,  */
+/* { dg-final { scan-assembler-not "cmp\t" } } */
+/* { dg-final { scan-assembler "\tneg\t" } } */
+

diff --git a/gcc/testsuite/gcc.target/aarch64/csel-neg-2.c b/gcc/testsuite/gcc.target/aarch64/csel-neg-2.c
new file mode 100644 (file)
index 0000000..72fe9b7
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/csel-neg-2.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* Disable phiopt as that will optimize away the `?:`,
+   want to test simplify-rtx */
+/* { dg-options "-O2 -ffast-math -fno-ssa-phiopt" } */
+
+/* PR rtl-optimization/58195 */
+
+float a2(float input)
+{
+  if (input == 0)
+    return 0;
+  return -input;
+}
+
+/* There should be no comparison against 0 here,  */
+/* { dg-final { scan-assembler-not "\tfcmp\t" } } */
+/* { dg-final { scan-assembler-not "\tfcsel\t" } } */
+/* { dg-final { scan-assembler "\tfneg\t" } } */
+