New version of the patch including the changes Jeff requested.
* Reformatted code.
* Including test cases (unfortunately requires lp64 although the
feature does not).
* Bootstrapped and regression tested on s390, s390x, x86_64.
On Wed, Apr 27, 2016 at 09:20:05AM +0100, Dominik Vogt wrote:
> The attached patch is a result of discussing an S/390 issue with
> "and with complement" in some cases.
>
> https://gcc.gnu.org/ml/gcc/2016-03/msg00163.html
> https://gcc.gnu.org/ml/gcc-patches/2016-04/msg01586.html
>
> Combine would merge a ZERO_EXTEND and a SET taking the known zero
> bits into account, resulting in an AND. Later on,
> make_compound_operation() fails to replace that with a ZERO_EXTEND
> which we get for free on S/390 but leaves the AND, eventually
> resulting in two consecutive AND instructions.
>
> The current code in make_compound_operation() that detects
> opportunities for ZERO_EXTEND does not work here because it does
> not take the known zero bits into account:
>
> /* If the constant is one less than a power of two, this might be
> representable by an extraction even if no shift is present.
> If it doesn't end up being a ZERO_EXTEND, we will ignore it unless
> we are in a COMPARE. */
> else if ((i = exact_log2 (UINTVAL (XEXP (x, 1)) + 1)) >= 0)
> new_rtx = make_extraction (mode,
> make_compound_operation (XEXP (x, 0),
> next_code),
> 0, NULL_RTX, i, 1, 0, in_code == COMPARE);
>
> An attempt to use the zero bits in the above conditions resulted
> in many situations that generated worse code, so the patch tries
> to fix this in a more conservative way. While the effect is
> completely positive on S/390, this will very likely have
> unforeseeable consequences on other targets.
>
> Bootstrapped and regression tested on s390 and s390x only at the
> moment.
Ciao
Dominik ^_^ ^_^
--
Dominik Vogt
IBM Germany
gcc/ChangeLog
* combine.c (make_compound_operation): Take known zero bits into
account when checking for possible zero_extend.
gcc/testsuite/ChangeLog
* gcc.dg/zero_bits_compound-1.c: New test.
* gcc.dg/zero_bits_compound-2.c: New test.
>From 515b9eadba2818c982cc8f5c7100b1da3b859713 Mon Sep 17 00:00:00 2001
From: Dominik Vogt <v...@linux.vnet.ibm.com>
Date: Tue, 12 Apr 2016 09:53:46 +0100
Subject: [PATCH] Take known zero bits into account when checking
extraction.
Allows AND Insns with a const_int operand to be expressed as ZERO_EXTEND if the
operand ist a power of 2 - 1 even with the known zero bits masked out.
---
gcc/combine.c | 38 +++++++++++++++++++++++++
gcc/testsuite/gcc.dg/zero_bits_compound-1.c | 43 +++++++++++++++++++++++++++++
gcc/testsuite/gcc.dg/zero_bits_compound-2.c | 38 +++++++++++++++++++++++++
3 files changed, 119 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/zero_bits_compound-1.c
create mode 100644 gcc/testsuite/gcc.dg/zero_bits_compound-2.c
diff --git a/gcc/combine.c b/gcc/combine.c
index 3554f51..46dd9c1 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -7988,6 +7988,44 @@ make_compound_operation (rtx x, enum rtx_code in_code)
next_code),
i, NULL_RTX, 1, 1, 0, 1);
+ /* If the one operand is a paradoxical subreg of a register or memory and
+ the constant (limited to the smaller mode) has only zero bits where
+ the sub expression has known zero bits, this can be expressed as
+ a zero_extend. */
+ else if (GET_CODE (XEXP (x, 0)) == SUBREG)
+ {
+ rtx sub;
+
+ sub = XEXP (XEXP (x, 0), 0);
+ machine_mode sub_mode = GET_MODE (sub);
+ if ((REG_P (sub) || MEM_P (sub))
+ && GET_MODE_PRECISION (sub_mode) < mode_width)
+ {
+ unsigned HOST_WIDE_INT mode_mask = GET_MODE_MASK (sub_mode);
+ unsigned HOST_WIDE_INT mask;
+
+ /* original AND constant with all the known zero bits set */
+ mask = UINTVAL (XEXP (x, 1)) | (~nonzero_bits (sub, sub_mode));
+ if ((mask & mode_mask) == mode_mask)
+ {
+ bool speed_p = optimize_insn_for_speed_p ();
+ rtx temp = gen_rtx_ZERO_EXTEND (mode, sub);
+ int cost_of_and;
+ int cost_of_zero_ext;
+
+ cost_of_and = rtx_cost (x, mode, in_code, 1, speed_p);
+ cost_of_zero_ext = rtx_cost (temp, mode, in_code, 1, speed_p);
+ if (cost_of_zero_ext <= cost_of_and)
+ {
+ new_rtx = make_compound_operation (sub, next_code);
+ new_rtx = make_extraction (mode, new_rtx, 0, 0,
+ GET_MODE_PRECISION (sub_mode),
+ 1, 0, in_code == COMPARE);
+ }
+ }
+ }
+ }
+
break;
case LSHIFTRT:
diff --git a/gcc/testsuite/gcc.dg/zero_bits_compound-1.c b/gcc/testsuite/gcc.dg/zero_bits_compound-1.c
new file mode 100644
index 0000000..72cc62c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/zero_bits_compound-1.c
@@ -0,0 +1,43 @@
+/* Test whether an AND mask or'ed with the know zero bits that equals a mode
+ mask is a candidate for zero extendion. */
+
+/* Note: This test requires that char, int and long have different sizes and the
+ target has a way to do 32 -> 64 bit zero extension other than AND. Targets
+ that fail the test because they do not satisfy these preconditions can skip
+ it. */
+
+/* { dg-do compile { target lp64 } } */
+/* { dg-options "-O3 -dP" } */
+
+unsigned long foo (unsigned char c)
+{
+ unsigned long l;
+ unsigned int i;
+
+ i = ((unsigned int)c) << 8;
+ i |= ((unsigned int)c) << 20;
+ asm volatile ("":::);
+ i = i & 0x0ff0ff00;
+ asm volatile ("":::);
+ l = (unsigned long)i;
+
+ return l;
+}
+
+unsigned long bar (unsigned char c)
+{
+ unsigned long l;
+ unsigned int i;
+
+ i = ((unsigned int)c) << 8;
+ i |= ((unsigned int)c) << 20;
+ asm volatile ("":::);
+ i = i & 0x0ffffff0;
+ asm volatile ("":::);
+ l = (unsigned long)i;
+
+ return l;
+}
+
+/* Check that no pattern containing an AND expression was used. */
+/* { dg-final { scan-assembler-not "\\(and:" } } */
diff --git a/gcc/testsuite/gcc.dg/zero_bits_compound-2.c b/gcc/testsuite/gcc.dg/zero_bits_compound-2.c
new file mode 100644
index 0000000..ac53f36
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/zero_bits_compound-2.c
@@ -0,0 +1,38 @@
+/* Test whether an AND mask or'ed with the know zero bits that equals a mode
+ mask is a candidate for zero extendion. */
+
+/* { dg-do compile { target lp64 } } */
+/* { dg-options "-O3 -dP" } */
+
+unsigned long foo (unsigned char c)
+{
+ unsigned long l;
+ unsigned int i;
+
+ i = ((unsigned int)c) << 8;
+ i |= ((unsigned int)c) << 20;
+ asm volatile ("":::);
+ i = i & 0x0fe0fe00;
+ asm volatile ("":::);
+ l = (unsigned long)i;
+
+ return l;
+}
+
+unsigned long bar (unsigned char c)
+{
+ unsigned long l;
+ unsigned int i;
+
+ i = ((unsigned int)c) << 8;
+ i |= ((unsigned int)c) << 20;
+ asm volatile ("":::);
+ i = i & 0x07f007f0;
+ asm volatile ("":::);
+ l = (unsigned long)i;
+
+ return l;
+}
+
+/* Check that an AND expression was used. */
+/* { dg-final { scan-assembler-times "\\(and:" 2 } } */
--
2.3.0
