tree-optimization/120031 - CTZ pattern matching fails a case

This PR is about the pattern matching in tree-ssa-forwprop.cc not
working for the fallback implementation in ZSTD which uses a cast
aroud the negation of the value to be tested.  There's a pattern
eliding casts in (T')-(T)x already but that only covered an
inner widening conversion.  The following extends this to other
conversions given the negation will then be carried out in an
unsigned type.

	PR tree-optimization/120031
	* match.pd ((nop_outer_cast)-(inner_cast)var -> -(outer_cast)(var)):
	Allow inner conversions that are not widenings when the outer
	type is unsigned.

	* gcc.target/i386/pr120031.c: New testcase.

diff --git a/gcc/match.pd b/gcc/match.pd
index a150de5184f66be1e250e5492829ea0ab7818757..ab496d923cc013a6b1be6e3ff5670fca9c353086 100644 (file)
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -1123,9 +1123,9 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 #endif
 
 /* (nop_outer_cast)-(inner_cast)var -> -(outer_cast)(var)
-   if var is smaller in precision.
-   This is always safe for both doing the negative in signed or unsigned
-   as the value for undefined will not show up.
+   If var is smaller in precision this is always safe for both doing
+   the negative in signed or unsigned as the value for undefined will not
+   show up.  Else it is safe if the negation is done in an unsigned type.
    Note the outer cast cannot be a boolean type as the only valid values
    are 0,-1/1 (depending on the signedness of the boolean) and the negative
    is there to get the correct value.  */
@@ -1133,7 +1133,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  (convert (negate:s@1 (convert:s @0)))
  (if (INTEGRAL_TYPE_P (type)
       && tree_nop_conversion_p (type, TREE_TYPE (@1))
-      && TYPE_PRECISION (type) > TYPE_PRECISION (TREE_TYPE (@0))
+      && (TYPE_PRECISION (type) > TYPE_PRECISION (TREE_TYPE (@0))
+         || TYPE_UNSIGNED (type))
       && TREE_CODE (type) != BOOLEAN_TYPE)
     (negate (convert @0))))
 

diff --git a/gcc/testsuite/gcc.target/i386/pr120031.c b/gcc/testsuite/gcc.target/i386/pr120031.c
new file mode 100644 (file)
index 0000000..e329cbc
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr120031.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mbmi" } */
+
+unsigned int
+ZSTD_countTrailingZeros32_fallback (unsigned int val)
+{
+  static const unsigned int DeBruijn[32]
+    = { 0, 1, 28, 2, 29, 14, 24, 3,
+       30, 22, 20, 15, 25, 17, 4, 8,
+       31, 27, 13, 23, 21, 19, 16, 7,
+       26, 12, 18, 6, 11, 5, 10, 9};
+  return DeBruijn[((unsigned int) ((val & -(int) val) * 0x077CB531U)) >> 27];
+}
+
+/* { dg-final { scan-assembler "tzcnt" } } */