[PATCH] middle-end: fix de-optimizations with bitclear patterns on signed values

[Tamar Christina]

Hi All,

During testing after rebasing to commit I noticed a failing testcase with the
bitmask compare patch.

Consider the following C++ testcase:

#include <compare>

#define A __attribute__((noipa))
A bool f5 (double i, double j) { auto c = i <=> j; return c >= 0; }

This turns into a comparison against chars, on systems where chars are signed
the pattern inserts an unsigned convert such that it's able to do the
transformation.

i.e.:

  # RANGE [-1, 2]
  # c$_M_value_22 = PHI <-1(3), 0(2), 2(5), 1(4)>
  # RANGE ~[3, 254]
  _11 = (unsigned char) c$_M_value_22;
  _19 = _11 <= 1;
  # .MEM_24 = VDEF <.MEM_6(D)>
  D.10434 ={v} {CLOBBER};
  # .MEM_14 = VDEF <.MEM_24>
  D.10407 ={v} {CLOBBER};
  # VUSE <.MEM_14>
  return _19;

instead of:

  # RANGE [-1, 2]
  # c$_M_value_5 = PHI <-1(3), 0(2), 2(5), 1(4)>
  # RANGE [-2, 2]
  _3 = c$_M_value_5 & -2;
  _19 = _3 == 0;
  # .MEM_24 = VDEF <.MEM_6(D)>
  D.10440 ={v} {CLOBBER};
  # .MEM_14 = VDEF <.MEM_24>
  D.10413 ={v} {CLOBBER};
  # VUSE <.MEM_14>
  return _19;

This causes much worse codegen under -ffast-math due to phiops no longer
recognizing the pattern.  It turns out that phiopts spaceship_replacement is
looking for the exact form that was just changed.

Trying to get it to recognize the new form is not trivial as the transformation
doesn't look to work when the thing it's pointing to is itself a phi-node.

Because of these issues this change delays the replacements until after loop
opts.  This fixes the failing C++ testcase.

Bootstrapped Regtested on aarch64-none-linux-gnu,
x86_64-pc-linux-gnu and no regressions.

Ok for master?

Thanks,
Tamar

gcc/ChangeLog:

	* match.pd: Delay bitmask compare pattern till after loop opts.

--- inline copy of patch -- 
diff --git a/gcc/match.pd b/gcc/match.pd
index 9532cae582e152cae6e22fcce95a9744a844e3c2..d26e498447fc25a327a42cc6a119c6153d09ba03 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -4945,7 +4945,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
       icmp (le le gt le gt)
  (simplify
   (cmp (bit_and:c@2 @0 cst@1) integer_zerop)
-   (with { tree csts = bitmask_inv_cst_vector_p (@1); }
+   (if (canonicalize_math_after_vectorization_p ())
+    (with { tree csts = bitmask_inv_cst_vector_p (@1); }
      (switch
       (if (csts && TYPE_UNSIGNED (TREE_TYPE (@1))
 	   && (VECTOR_TYPE_P (TREE_TYPE (@1)) || single_use (@2)))
@@ -4954,7 +4955,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 	   && (cmp == EQ_EXPR || cmp == NE_EXPR)
 	   && (VECTOR_TYPE_P (TREE_TYPE (@1)) || single_use (@2)))
        (with { tree utype = unsigned_type_for (TREE_TYPE (@1)); }
-	(icmp (convert:utype @0) { csts; }))))))))
+	(icmp (convert:utype @0) { csts; })))))))))
 
 /* -A CMP -B -> B CMP A.  */
 (for cmp (tcc_comparison)


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