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 --git a/gcc/match.pd b/gcc/match.pd
index e7d10f427a94303378d4c28350059bd9fcb690d8..e32bda64e6440ffb8a4d1adeb8e77d14bb2a7d50 100644 (file)
--- 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 (file)
index 0000000..43fbcf7
--- /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" } } */