PR target/113560: Enhance is_widening_mult_rhs_p.

This patch resolves PR113560, a code quality regression from GCC12
affecting x86_64, by enhancing the middle-end's tree-ssa-math-opts.cc
to recognize more instances of widening multiplications.

The widening multiplication perception code identifies cases like:

	_1 = (unsigned __int128) x;
	__res = _1 * 100;

but in the reported test case, the original input looks like:

	_1 = (unsigned long long) x;
	_2 = (unsigned __int128) _1;
	__res = _2 * 100;

which gets optimized by constant folding during tree-ssa to:

	_2 = x & 18446744073709551615;  // x & 0xffffffffffffffff
	__res = _2 * 100;

where the BIT_AND_EXPR hides (has consumed) the extension operation.
This reveals the more general deficiency (missed optimization
opportunity) in widening multiplication perception that additionally
both

__int128 foo(__int128 x, __int128 y) {
  return (x & 1000) * (y & 1000)
}

and

unsigned __int128 bar(unsigned __int128 x, unsigned __int128) {
  return (x >> 80) * (y >> 80);
}

should be recognized as widening multiplications.  Hence rather than
test explicitly for BIT_AND_EXPR (as in the first version of this patch)
the more general solution is to make use of range information, as
provided by tree_non_zero_bits.

As a demonstration of the observed improvements, function foo above
currently with -O2 compiles on x86_64 to:

foo:	movq    %rdi, %rsi
        movq    %rdx, %r8
        xorl    %edi, %edi
        xorl    %r9d, %r9d
        andl    $1000, %esi
        andl    $1000, %r8d
        movq    %rdi, %rcx
        movq    %r9, %rdx
        imulq   %rsi, %rdx
        movq    %rsi, %rax
        imulq   %r8, %rcx
        addq    %rdx, %rcx
        mulq    %r8
        addq    %rdx, %rcx
        movq    %rcx, %rdx
        ret

with this patch, GCC recognizes the *w and instead generates:

foo:    movq    %rdi, %rsi
        movq    %rdx, %r8
        andl    $1000, %esi
        andl    $1000, %r8d
        movq    %rsi, %rax
        imulq   %r8
        ret

which is perhaps easier to understand at the tree-level where

__int128 foo (__int128 x, __int128 y)
{
  __int128 _1;
  __int128 _2;
  __int128 _5;

  <bb 2> [local count: 1073741824]:
  _1 = x_3(D) & 1000;
  _2 = y_4(D) & 1000;
  _5 = _1 * _2;
  return _5;

}

gets transformed to:

__int128 foo (__int128 x, __int128 y)
{
  __int128 _1;
  __int128 _2;
  __int128 _5;
  signed long _7;
  signed long _8;

  <bb 2> [local count: 1073741824]:
  _1 = x_3(D) & 1000;
  _2 = y_4(D) & 1000;
  _7 = (signed long) _1;
  _8 = (signed long) _2;
  _5 = _7 w* _8;
  return _5;
}

2023-02-01  Roger Sayle  <roger@nextmovesoftware.com>
	    Richard Biener  <rguenther@suse.de>

gcc/ChangeLog
	PR target/113560
	* tree-ssa-math-opts.cc (is_widening_mult_rhs_p): Use range
	information via tree_non_zero_bits to check if this operand
	is suitably extended for a widening (or highpart) multiplication.
	(convert_mult_to_widen): Insert explicit casts if the RHS or LHS
	isn't already of the claimed type.

gcc/testsuite/ChangeLog
	PR target/113560
	* g++.target/i386/pr113560.C: New test case.
	* gcc.target/i386/pr113560.c: Likewise.
	* gcc.dg/pr87954.c: Update test case.

diff --git a/gcc/testsuite/g++.target/i386/pr113560.C b/gcc/testsuite/g++.target/i386/pr113560.C
new file mode 100644 (file)
index 0000000..179b68f
--- /dev/null
+++ b/gcc/testsuite/g++.target/i386/pr113560.C
@@ -0,0 +1,19 @@
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-options "-Ofast -std=c++23 -march=znver4" } */
+
+#include <immintrin.h>
+auto f(char *buf, unsigned long long in) noexcept
+{
+    unsigned long long hi{};
+    auto lo{_mulx_u64(in, 0x2af31dc462ull, &hi)};
+    lo = _mulx_u64(lo, 100, &hi);
+    __builtin_memcpy(buf + 2, &hi, 2);
+    return buf + 10;
+}
+
+/* { dg-final { scan-assembler-times "mulx" 1 } } */
+/* { dg-final { scan-assembler-times "mulq" 1 } } */
+/* { dg-final { scan-assembler-not "addq" } } */
+/* { dg-final { scan-assembler-not "adcq" } } */
+/* { dg-final { scan-assembler-not "salq" } } */
+/* { dg-final { scan-assembler-not "shldq" } } */

diff --git a/gcc/testsuite/gcc.dg/pr87954.c b/gcc/testsuite/gcc.dg/pr87954.c
index 620657cb1f5d3dc507eb1972074dd5b04b9924e2..80d0543bbb389f1188fc56e8acd1dead3383fd63 100644 (file)
--- a/gcc/testsuite/gcc.dg/pr87954.c
+++ b/gcc/testsuite/gcc.dg/pr87954.c
@@ -18,4 +18,4 @@ imul(unsigned int flags)
   return type_dma + (is_rec * !is_dma) * KMALLOC_RECLAIM;
 }
 
-/* { dg-final { scan-tree-dump-times { \* } 1 "optimized" } } */
+/* { dg-final { scan-tree-dump-times { \*w? |WIDEN_MULT_PLUS_EXPR} 1 "optimized" } } */

diff --git a/gcc/testsuite/gcc.target/i386/pr113560.c b/gcc/testsuite/gcc.target/i386/pr113560.c
new file mode 100644 (file)
index 0000000..ac2e01a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr113560.c
@@ -0,0 +1,17 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2" } */
+
+unsigned __int128 foo(unsigned __int128 x, unsigned __int128 y)
+{
+  return (x & 1000) * (y & 1000);
+}
+
+__int128 bar(__int128 x, __int128 y)
+{
+  return (x & 1000) * (y & 1000);
+}
+
+/* { dg-final { scan-assembler-times "\tmulq" 1 } } */
+/* { dg-final { scan-assembler-times "\timulq" 1 } } */
+/* { dg-final { scan-assembler-not "addq" } } */
+/* { dg-final { scan-assembler-not "xorl" } } */

diff --git a/gcc/tree-ssa-math-opts.cc b/gcc/tree-ssa-math-opts.cc
index 2db26e4ed4868aa1baf2fa88a0f327f0bd4ea56f..cffe7573f794731629335965eb2a0f45b4d47857 100644 (file)
--- a/gcc/tree-ssa-math-opts.cc
+++ b/gcc/tree-ssa-math-opts.cc
@@ -2552,12 +2552,47 @@ is_widening_mult_rhs_p (tree type, tree rhs, tree *type_out,
 
   if (TREE_CODE (rhs) == SSA_NAME)
     {
+      /* Use tree_non_zero_bits to see if this operand is zero_extended
+        for unsigned widening multiplications or non-negative for
+        signed widening multiplications.  */
+      if (TREE_CODE (type) == INTEGER_TYPE
+         && (TYPE_PRECISION (type) & 1) == 0
+         && int_mode_for_size (TYPE_PRECISION (type) / 2, 1).exists ())
+       {
+         unsigned int prec = TYPE_PRECISION (type);
+         unsigned int hprec = prec / 2;
+         wide_int bits = wide_int::from (tree_nonzero_bits (rhs), prec,
+                                         TYPE_SIGN (TREE_TYPE (rhs)));
+         if (TYPE_UNSIGNED (type)
+             && wi::bit_and (bits, wi::mask (hprec, true, prec)) == 0)
+           {
+             *type_out = build_nonstandard_integer_type (hprec, true);
+             /* X & MODE_MASK can be simplified to (T)X.  */
+             stmt = SSA_NAME_DEF_STMT (rhs);
+             if (is_gimple_assign (stmt)
+                 && gimple_assign_rhs_code (stmt) == BIT_AND_EXPR
+                 && TREE_CODE (gimple_assign_rhs2 (stmt)) == INTEGER_CST
+                 && wi::to_wide (gimple_assign_rhs2 (stmt))
+                    == wi::mask (hprec, false, prec))
+               *new_rhs_out = gimple_assign_rhs1 (stmt);
+             else
+               *new_rhs_out = rhs;
+             return true;
+           }
+         else if (!TYPE_UNSIGNED (type)
+                  && wi::bit_and (bits, wi::mask (hprec - 1, true, prec)) == 0)
+           {
+             *type_out = build_nonstandard_integer_type (hprec, false);
+             *new_rhs_out = rhs;
+             return true;
+           }
+       }
+
       stmt = SSA_NAME_DEF_STMT (rhs);
       if (is_gimple_assign (stmt))
        {
-         if (! widening_mult_conversion_strippable_p (type, stmt))
-           rhs1 = rhs;
-         else
+
+         if (widening_mult_conversion_strippable_p (type, stmt))
            {
              rhs1 = gimple_assign_rhs1 (stmt);
 
@@ -2568,6 +2603,8 @@ is_widening_mult_rhs_p (tree type, tree rhs, tree *type_out,
                  return true;
                }
            }
+         else
+           rhs1 = rhs;
        }
       else
        rhs1 = rhs;
@@ -2827,12 +2864,16 @@ convert_mult_to_widen (gimple *stmt, gimple_stmt_iterator *gsi)
   if (2 * actual_precision > TYPE_PRECISION (type))
     return false;
   if (actual_precision != TYPE_PRECISION (type1)
-      || from_unsigned1 != TYPE_UNSIGNED (type1))
+      || from_unsigned1 != TYPE_UNSIGNED (type1)
+      || (TREE_TYPE (rhs1) != type1
+         && TREE_CODE (rhs1) != INTEGER_CST))
     rhs1 = build_and_insert_cast (gsi, loc,
                                  build_nonstandard_integer_type
                                    (actual_precision, from_unsigned1), rhs1);
   if (actual_precision != TYPE_PRECISION (type2)
-      || from_unsigned2 != TYPE_UNSIGNED (type2))
+      || from_unsigned2 != TYPE_UNSIGNED (type2)
+      || (TREE_TYPE (rhs2) != type2
+         && TREE_CODE (rhs2) != INTEGER_CST))
     rhs2 = build_and_insert_cast (gsi, loc,
                                  build_nonstandard_integer_type
                                    (actual_precision, from_unsigned2), rhs2);
@@ -3046,7 +3087,7 @@ convert_plusminus_to_widen (gimple_stmt_iterator *gsi, gimple *stmt,
       || from_unsigned1 != TYPE_UNSIGNED (type1))
     mult_rhs1 = build_and_insert_cast (gsi, loc,
                                       build_nonstandard_integer_type
-                                        (actual_precision, from_unsigned1),
+                                        (actual_precision, from_unsigned1),
                                       mult_rhs1);
   if (actual_precision != TYPE_PRECISION (type2)
       || from_unsigned2 != TYPE_UNSIGNED (type2))