[PATCH] phiopt: Optimize x < 0 ? ~y : y to (x >> 31) ^ y [PR96928]
Jakub Jelinek
jakub@redhat.com
Tue Jan 5 08:56:48 GMT 2021
Hi!
As requested in the PR, the one's complement abs can be done more
efficiently without cmov or branching.
Had to change the ifcvt-onecmpl-abs-1.c testcase, we no longer optimize
it in ifcvt, on x86_64 with -m32 we generate in the end the exact same
code, but with -m64:
movl %edi, %eax
- notl %eax
- cmpl %edi, %eax
- cmovl %edi, %eax
+ sarl $31, %eax
+ xorl %edi, %eax
ret
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2021-01-05 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/96928
* tree-ssa-phiopt.c (xor_replacement): New function.
(tree_ssa_phiopt_worker): Call it.
* gcc.dg/tree-ssa/pr96928.c: New test.
* gcc.target/i386/ifcvt-onecmpl-abs-1.c: Remove -fdump-rtl-ce1,
instead of scanning rtl dump for ifcvt message check assembly
for xor instruction.
--- gcc/tree-ssa-phiopt.c.jj 2021-01-04 10:25:38.638236032 +0100
+++ gcc/tree-ssa-phiopt.c 2021-01-04 15:29:30.050005505 +0100
@@ -62,6 +62,8 @@ static bool minmax_replacement (basic_bl
edge, edge, gimple *, tree, tree);
static bool abs_replacement (basic_block, basic_block,
edge, edge, gimple *, tree, tree);
+static bool xor_replacement (basic_block, basic_block,
+ edge, edge, gimple *, tree, tree);
static bool cond_removal_in_popcount_clz_ctz_pattern (basic_block, basic_block,
edge, edge, gimple *,
tree, tree);
@@ -346,6 +348,9 @@ tree_ssa_phiopt_worker (bool do_store_el
else if (abs_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
cfgchanged = true;
else if (!early_p
+ && xor_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
+ cfgchanged = true;
+ else if (!early_p
&& cond_removal_in_popcount_clz_ctz_pattern (bb, bb1, e1,
e2, phi, arg0,
arg1))
@@ -2097,6 +2102,109 @@ abs_replacement (basic_block cond_bb, ba
/* Note that we optimized this PHI. */
return true;
}
+
+/* Optimize x < 0 ? ~y : y into (x >> (prec-1)) ^ y. */
+
+static bool
+xor_replacement (basic_block cond_bb, basic_block middle_bb,
+ edge e0 ATTRIBUTE_UNUSED, edge e1,
+ gimple *phi, tree arg0, tree arg1)
+{
+ if (!INTEGRAL_TYPE_P (TREE_TYPE (arg1)))
+ return false;
+
+ /* OTHER_BLOCK must have only one executable statement which must have the
+ form arg0 = ~arg1 or arg1 = ~arg0. */
+
+ gimple *assign = last_and_only_stmt (middle_bb);
+ /* If we did not find the proper one's complement assignment, then we cannot
+ optimize. */
+ if (assign == NULL)
+ return false;
+
+ /* If we got here, then we have found the only executable statement
+ in OTHER_BLOCK. If it is anything other than arg = ~arg1 or
+ arg1 = ~arg0, then we cannot optimize. */
+ if (!is_gimple_assign (assign))
+ return false;
+
+ if (gimple_assign_rhs_code (assign) != BIT_NOT_EXPR)
+ return false;
+
+ tree lhs = gimple_assign_lhs (assign);
+ tree rhs = gimple_assign_rhs1 (assign);
+
+ /* The assignment has to be arg0 = -arg1 or arg1 = -arg0. */
+ if (!(lhs == arg0 && rhs == arg1) && !(lhs == arg1 && rhs == arg0))
+ return false;
+
+ gimple *cond = last_stmt (cond_bb);
+ tree result = PHI_RESULT (phi);
+
+ /* Only relationals comparing arg[01] against zero are interesting. */
+ enum tree_code cond_code = gimple_cond_code (cond);
+ if (cond_code != LT_EXPR && cond_code != GE_EXPR)
+ return false;
+
+ /* Make sure the conditional is x OP 0. */
+ tree clhs = gimple_cond_lhs (cond);
+ if (TREE_CODE (clhs) != SSA_NAME
+ || !INTEGRAL_TYPE_P (TREE_TYPE (clhs))
+ || TYPE_UNSIGNED (TREE_TYPE (clhs))
+ || TYPE_PRECISION (TREE_TYPE (clhs)) != TYPE_PRECISION (TREE_TYPE (arg1))
+ || !integer_zerop (gimple_cond_rhs (cond)))
+ return false;
+
+ /* We need to know which is the true edge and which is the false
+ edge so that we know if have xor or inverted xor. */
+ edge true_edge, false_edge;
+ extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);
+
+ /* For GE_EXPR, if the true edge goes to OTHER_BLOCK, then we
+ will need to invert the result. Similarly for LT_EXPR if
+ the false edge goes to OTHER_BLOCK. */
+ edge e;
+ if (cond_code == GE_EXPR)
+ e = true_edge;
+ else
+ e = false_edge;
+
+ bool invert = e->dest == middle_bb;
+
+ result = duplicate_ssa_name (result, NULL);
+
+ gimple_stmt_iterator gsi = gsi_last_bb (cond_bb);
+
+ int prec = TYPE_PRECISION (TREE_TYPE (clhs));
+ gimple *new_stmt
+ = gimple_build_assign (make_ssa_name (TREE_TYPE (clhs)), RSHIFT_EXPR, clhs,
+ build_int_cst (integer_type_node, prec - 1));
+ gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
+
+ if (!useless_type_conversion_p (TREE_TYPE (result), TREE_TYPE (clhs)))
+ {
+ new_stmt = gimple_build_assign (make_ssa_name (TREE_TYPE (result)),
+ NOP_EXPR, gimple_assign_lhs (new_stmt));
+ gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
+ }
+ lhs = gimple_assign_lhs (new_stmt);
+
+ if (invert)
+ {
+ new_stmt = gimple_build_assign (make_ssa_name (TREE_TYPE (result)),
+ BIT_NOT_EXPR, rhs);
+ gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
+ rhs = gimple_assign_lhs (new_stmt);
+ }
+
+ new_stmt = gimple_build_assign (result, BIT_XOR_EXPR, lhs, rhs);
+ gsi_insert_before (&gsi, new_stmt, GSI_NEW_STMT);
+
+ replace_phi_edge_with_variable (cond_bb, e1, phi, result);
+
+ /* Note that we optimized this PHI. */
+ return true;
+}
/* Auxiliary functions to determine the set of memory accesses which
can't trap because they are preceded by accesses to the same memory
--- gcc/testsuite/gcc.dg/tree-ssa/pr96928.c.jj 2021-01-04 15:41:34.803857493 +0100
+++ gcc/testsuite/gcc.dg/tree-ssa/pr96928.c 2021-01-04 15:43:16.794710865 +0100
@@ -0,0 +1,38 @@
+/* PR tree-optimization/96928 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-phiopt2" } */
+/* { dg-final { scan-tree-dump-times " = a_\[0-9]*\\\(D\\\) >> " 5 "phiopt2" } } */
+/* { dg-final { scan-tree-dump-times " = ~c_\[0-9]*\\\(D\\\);" 1 "phiopt2" } } */
+/* { dg-final { scan-tree-dump-times " = ~" 1 "phiopt2" } } */
+/* { dg-final { scan-tree-dump-times " = \[abc_0-9\\\(\\\)D]* \\\^ " 5 "phiopt2" } } */
+/* { dg-final { scan-tree-dump-not "a < 0" "phiopt2" } } */
+
+int
+foo (int a)
+{
+ return a < 0 ? ~a : a;
+}
+
+int
+bar (int a, int b)
+{
+ return a < 0 ? ~b : b;
+}
+
+unsigned
+baz (int a, unsigned int b)
+{
+ return a < 0 ? ~b : b;
+}
+
+unsigned
+qux (int a, unsigned int c)
+{
+ return a >= 0 ? ~c : c;
+}
+
+int
+corge (int a, int b)
+{
+ return a >= 0 ? b : ~b;
+}
--- gcc/testsuite/gcc.target/i386/ifcvt-onecmpl-abs-1.c.jj 2020-01-12 11:54:37.946390280 +0100
+++ gcc/testsuite/gcc.target/i386/ifcvt-onecmpl-abs-1.c 2021-01-05 09:39:14.326747916 +0100
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O2 -fdump-rtl-ce1" } */
+/* { dg-options "-O2" } */
/* Check code generation for one's complement version of abs */
@@ -10,4 +10,4 @@ int onecmplabs(int x)
return x;
}
-/* { dg-final { scan-rtl-dump "succeeded through noce_try_abs" "ce1" } } */
+/* { dg-final { scan-assembler "\txor" } } */
Jakub
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