tree-optimization/88540 - FP x > y ? x : y if-conversion without -ffa…

…st-math

The following makes sure that FP x > y ? x : y style max/min operations
are if-converted at the GIMPLE level.  While we can neither match
it to MAX_EXPR nor .FMAX as both have different semantics with IEEE
than the ternary ?: operation we can make sure to maintain this form
as a COND_EXPR so backends have the chance to match this to instructions
their ISA offers.

The patch does this in phiopt where we recognize min/max and instead
of giving up when we have to honor NaNs we alter the generated code
to a COND_EXPR.

This resolves PR88540 and we can then SLP vectorize the min operation
for its testcase.  It also resolves part of the regressions observed
with the change matching bit-inserts of bit-field-refs to vec_perm.

Expansion from a COND_EXPR rather than from compare-and-branch
regresses gcc.target/i386/pr54855-13.c and gcc.target/i386/pr54855-9.c
by producing extra moves while the corresponding min/max operations
are now already synthesized by RTL expansion, register selection
isn't optimal.  This can be also provoked without this change by
altering the operand order in the source.

It regresses gcc.target/i386/pr110170.c where we end up CSEing the
condition which makes RTL expansion no longer produce the min/max
directly and code generation is obfuscated enough to confuse
RTL if-conversion.

It also regresses gcc.target/i386/ssefp-[12].c where oddly one
variant isn't if-converted and ix86_expand_fp_movcc doesn't
match directly (the FP constants get expanded twice).  A fix
could be in emit_conditional_move where both prepare_cmp_insn
and emit_conditional_move_1 force the constants to (different)
registers.

Otherwise bootstrapped and tested on x86_64-unknown-linux-gnu.

	PR tree-optimization/88540
	* tree-ssa-phiopt.cc (minmax_replacement): Do not give up
	with NaNs but handle the simple case by if-converting to a
	COND_EXPR.

	* gcc.target/i386/pr88540.c: New testcase.
	* gcc.target/i386/pr54855-12.c: Adjust.
	* gcc.target/i386/pr54855-13.c: Likewise.

gcc/testsuite/gcc.target/i386/pr54855-12.c

@@ -1,6 +1,6 @@
 /* { dg-do compile } */
 /* { dg-options "-O2 -mavx512fp16" } */
-/* { dg-final { scan-assembler-times "vmaxsh\[ \\t\]" 1 } } */
+/* { dg-final { scan-assembler-times "vm\[ai\]\[nx\]sh\[ \\t\]" 1 } } */
 /* { dg-final { scan-assembler-not "vcomish\[ \\t\]" } } */
 /* { dg-final { scan-assembler-not "vmovsh\[ \\t\]" { target { ! ia32 } } } } */
 

gcc/testsuite/gcc.target/i386/pr54855-13.c

@@ -1,6 +1,6 @@
 /* { dg-do compile } */
 /* { dg-options "-O2 -mavx512fp16" } */
-/* { dg-final { scan-assembler-times "vmaxsh\[ \\t\]" 1 } } */
+/* { dg-final { scan-assembler-times "vm\[ai\]\[nx\]sh\[ \\t\]" 1 } } */
 /* { dg-final { scan-assembler-not "vcomish\[ \\t\]" } } */
 /* { dg-final { scan-assembler-not "vmovsh\[ \\t\]" { target { ! ia32 } } } } */
 

gcc/testsuite/gcc.target/i386/pr88540.c

@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -msse2" } */
+
+void test(double* __restrict d1, double* __restrict d2, double* __restrict d3)
+{
+  for (int n = 0; n < 2; ++n)
+    d3[n] = d1[n] < d2[n] ? d1[n] : d2[n];
+}
+
+/* { dg-final { scan-assembler "minpd" } } */

gcc/tree-ssa-phiopt.cc

@@ -1570,10 +1570,6 @@ minmax_replacement (basic_block cond_bb, basic_block middle_bb, basic_block alt_
 
   tree type = TREE_TYPE (PHI_RESULT (phi));
 
-  /* The optimization may be unsafe due to NaNs.  */
-  if (HONOR_NANS (type) || HONOR_SIGNED_ZEROS (type))
-    return false;
-
   gcond *cond = as_a <gcond *> (*gsi_last_bb (cond_bb));
   enum tree_code cmp = gimple_cond_code (cond);
   tree rhs = gimple_cond_rhs (cond);
@@ -1760,6 +1756,9 @@ minmax_replacement (basic_block cond_bb, basic_block middle_bb, basic_block alt_
       else
 	return false;
     }
+  else if (HONOR_NANS (type) || HONOR_SIGNED_ZEROS (type))
+    /* The optimization may be unsafe due to NaNs.  */
+    return false;
   else if (middle_bb != alt_middle_bb && threeway_p)
     {
       /* Recognize the following case:
@@ -2093,7 +2092,19 @@ minmax_replacement (basic_block cond_bb, basic_block middle_bb, basic_block alt_
   /* Emit the statement to compute min/max.  */
   gimple_seq stmts = NULL;
   tree phi_result = PHI_RESULT (phi);
-  result = gimple_build (&stmts, minmax, TREE_TYPE (phi_result), arg0, arg1);
+
+  /* When we can't use a MIN/MAX_EXPR still make sure the expression
+     stays in a form to be recognized by ISA that map to IEEE x > y ? x : y
+     semantics (that's not IEEE max semantics).  */
+  if (HONOR_NANS (type) || HONOR_SIGNED_ZEROS (type))
+    {
+      result = gimple_build (&stmts, cmp, boolean_type_node,
+			     gimple_cond_lhs (cond), rhs);
+      result = gimple_build (&stmts, COND_EXPR, TREE_TYPE (phi_result),
+			     result, arg_true, arg_false);
+    }
+  else
+    result = gimple_build (&stmts, minmax, TREE_TYPE (phi_result), arg0, arg1);
 
   gsi = gsi_last_bb (cond_bb);
   gsi_insert_seq_before (&gsi, stmts, GSI_NEW_STMT);