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* [gcc r13-2048] PR tree-optimization/64992: (B << 2) != 0 is B when B is Boolean.
@ 2022-08-15 16:40 Roger Sayle
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From: Roger Sayle @ 2022-08-15 16:40 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:418b71c0d535bf91df78bad2e198c57934682eaa
commit r13-2048-g418b71c0d535bf91df78bad2e198c57934682eaa
Author: Roger Sayle <roger@nextmovesoftware.com>
Date: Mon Aug 15 17:39:47 2022 +0100
PR tree-optimization/64992: (B << 2) != 0 is B when B is Boolean.
This patch resolves both PR tree-optimization/64992 and PR
tree-optimization/98956 which are missed optimization enhancement
request, for which Andrew Pinski already has a proposed solution
(related to a fix for PR tree-optimization/98954). Yesterday,
I proposed an alternate improved patch for PR98954, which although
superior in most respects, alas didn't address this case [which
doesn't include a BIT_AND_EXPR], hence this follow-up fix.
For many functions, F(B), of a (zero-one) Boolean value B, the
expression F(B) != 0 can often be simplified to just B. Hence
"(B * 5) != 0" is B, "-B != 0" is B, "bswap(B) != 0" is B,
"(B >>r 3) != 0" is B. These are all currently optimized by GCC,
with the strange exception of left shifts by a constant (possibly
due to the undefined/implementation defined behaviour when the
shift constant is larger than the first operand's precision).
This patch adds support for this particular case, when the shift
constant is valid.
2022-08-15 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
PR tree-optimization/64992
PR tree-optimization/98956
* match.pd (ne (lshift @0 @1) 0): Simplify (X << C) != 0 to X
when X is zero_one_valued_p and the shift constant C is valid.
(eq (lshift @0 @1) 0): Likewise, simplify (X << C) == 0 to !X
when X is zero_one_valued_p and the shift constant C is valid.
gcc/testsuite/ChangeLog
PR tree-optimization/64992
* gcc.dg/pr64992.c: New test case.
Diff:
---
gcc/match.pd | 20 ++++++++++++++++++++
gcc/testsuite/gcc.dg/pr64992.c | 7 +++++++
2 files changed, 27 insertions(+)
diff --git a/gcc/match.pd b/gcc/match.pd
index e7d10f427a9..e32bda64e64 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -1920,6 +1920,26 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
&& TYPE_PRECISION (type) <= TYPE_PRECISION (TREE_TYPE (@0)))
(mult (convert @1) (convert @2))))
+/* (X << C) != 0 can be simplified to X, when C is zero_one_valued_p.
+ Check that the shift is well-defined (C is less than TYPE_PRECISION)
+ as some targets (such as x86's SSE) may return zero for larger C. */
+(simplify
+ (ne (lshift zero_one_valued_p@0 INTEGER_CST@1) integer_zerop@2)
+ (if (tree_fits_shwi_p (@1)
+ && tree_to_shwi (@1) > 0
+ && tree_to_shwi (@1) < TYPE_PRECISION (TREE_TYPE (@0)))
+ (convert @0)))
+
+/* (X << C) == 0 can be simplified to X == 0, when C is zero_one_valued_p.
+ Check that the shift is well-defined (C is less than TYPE_PRECISION)
+ as some targets (such as x86's SSE) may return zero for larger C. */
+(simplify
+ (eq (lshift zero_one_valued_p@0 INTEGER_CST@1) integer_zerop@2)
+ (if (tree_fits_shwi_p (@1)
+ && tree_to_shwi (@1) > 0
+ && tree_to_shwi (@1) < TYPE_PRECISION (TREE_TYPE (@0)))
+ (eq @0 @2)))
+
/* Convert ~ (-A) to A - 1. */
(simplify
(bit_not (convert? (negate @0)))
diff --git a/gcc/testsuite/gcc.dg/pr64992.c b/gcc/testsuite/gcc.dg/pr64992.c
new file mode 100644
index 00000000000..43fbcf7ac50
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr64992.c
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+_Bool foo(_Bool x) { return (x << 2) != 0; }
+_Bool bar(_Bool x) { return (x << 2) == 0; }
+
+/* { dg-final { scan-tree-dump-not " << " "optimized" } } */
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