On Tue, 22 Feb 2022 at 11:57, Zhao Wei Liew <zhaoweil...@gmail.com> wrote:
>
> Hi,
>
> This is a partial optimization for PR103855.
>
> Initially, I looked into optimizing RTL generation or a more complex
> GIMPLE transformation so that we could optimize other cases as well,
> such as ((unsigned long long) short / int).
>
> However, that is a bit too complex for now. While I continue to look
> into that change, I've decided to implement this simpler match.pd
> transformation.
>
> Greatly appreciate any feedback on this patch or guidance for
> implementing the more advanced optimizations!
>
> Thanks,
> Zhao Wei
Sorry, the original patch wasn't recognized as a text file. I've added
a .txt extension to make it explicit.
From dd3bb05cd7be72d080598cb693549ac74d5cb02d Mon Sep 17 00:00:00 2001
From: Zhao Wei Liew <zhaoweil...@gmail.com>
Date: Sat, 19 Feb 2022 16:28:38 +0800
Subject: [PATCH] tree-optimization: [PR103855] Fold (type)X / (type)Y
This pattern converts (trunc_div (convert a) (convert b)) to
(convert (trunc_div a b)) when:
1. type, a, and b all have unsigned integeral types
2. a and b have the same type precision
3. type has type precision at least as larger as a and b
This is useful as wider divisions are typically more expensive.
To illustrate the effects, consider the following code snippet:
unsigned long long f(unsigned int a, unsigned int b) {
unsigned long long all = a;
return all / b;
}
Without the pattern, g++ -std=c++20 -O2 generates the following
assembly:
f(unsigned int, unsigned int):
mov eax, edi
mov esi, esi
xor edx, edx
div rsi
ret
With the pattern, it generates this:
f(unsigned int, unsigned int):
mov eax, edi
xor edx, edx
div esi
ret
This is identical to what clang++ -std=c++20 -O2 generates.
Bootstrapped and regression tested on x86_64-pc-linux-gnu.
Signed-off-by: Zhao Wei Liew <zhaoweil...@gmail.com>
PR tree-optimization/103855
gcc/ChangeLog:
* match.pd: Add pattern for (type)X / (type)Y.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/divide-8.c: New test.
* gcc.dg/tree-ssa/divide-9.c: New test.
---
gcc/match.pd | 15 +++++++++++++++
gcc/testsuite/gcc.dg/tree-ssa/divide-8.c | 9 +++++++++
gcc/testsuite/gcc.dg/tree-ssa/divide-9.c | 9 +++++++++
3 files changed, 33 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/divide-8.c
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/divide-9.c
diff --git a/gcc/match.pd b/gcc/match.pd
index 10f62284862..393b43756dd 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -684,6 +684,21 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(if (INTEGRAL_TYPE_P (type) || VECTOR_INTEGER_TYPE_P (type))
(convert (trunc_mod @0 @1))))
+/* (type)X / (type)Y -> (type)(X / Y)
+ when the resulting type is at least precise as the original types
+ and when all the types are unsigned integral types. */
+(simplify
+ (trunc_div (convert @0) (convert @1))
+ (if (INTEGRAL_TYPE_P (type)
+ && INTEGRAL_TYPE_P (TREE_TYPE (@0))
+ && INTEGRAL_TYPE_P (TREE_TYPE (@1))
+ && TYPE_UNSIGNED (type)
+ && TYPE_UNSIGNED (TREE_TYPE (@0))
+ && TYPE_UNSIGNED (TREE_TYPE (@1))
+ && TYPE_PRECISION (TREE_TYPE (@0)) == TYPE_PRECISION (TREE_TYPE (@1))
+ && TYPE_PRECISION (type) >= TYPE_PRECISION (TREE_TYPE (@0)))
+ (convert (trunc_div @0 @1))))
+
/* x * (1 + y / x) - y -> x - y % x */
(simplify
(minus (mult:cs @0 (plus:s (trunc_div:s @1 @0) integer_onep)) @1)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/divide-8.c
b/gcc/testsuite/gcc.dg/tree-ssa/divide-8.c
new file mode 100644
index 00000000000..dc3dc9ca769
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/divide-8.c
@@ -0,0 +1,9 @@
+/* PR tree-optimization/103855 */
+/* { dg-options "-O -fdump-tree-optimized" } */
+
+unsigned int f(unsigned int a, unsigned int b) {
+ unsigned long long all = a;
+ return all / b;
+}
+
+/* { dg-final { scan-tree-dump-not "\\\(long long unsigned int\\\)"
"optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/divide-9.c
b/gcc/testsuite/gcc.dg/tree-ssa/divide-9.c
new file mode 100644
index 00000000000..6986b5484e4
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/divide-9.c
@@ -0,0 +1,9 @@
+/* PR tree-optimization/103855 */
+/* { dg-options "-O -fdump-tree-optimized" } */
+
+unsigned long long f(unsigned int a, unsigned int b) {
+ unsigned long long all = a;
+ return all / b;
+}
+
+/* { dg-final { scan-tree-dump-times "\\\(long long unsigned int\\\)" 1
"optimized" } } */
--
2.35.1
