[gcc r14-7133] LOOP-UNROLL: Leverage HAS_SIGNED_ZERO for var expansion

[Pan Li]

https://gcc.gnu.org/g:b89ef3d40afc4604c279e8802bf279f6e4060f67

commit r14-7133-gb89ef3d40afc4604c279e8802bf279f6e4060f67
Author: Pan Li <pan2.li@intel.com>
Date:   Wed Jan 10 20:57:17 2024 +0800

    LOOP-UNROLL: Leverage HAS_SIGNED_ZERO for var expansion
    
    The insert_var_expansion_initialization depends on the
    HONOR_SIGNED_ZEROS to initialize the unrolling variables
    to +0.0f when -0.0f and no-signed-option.  Unfortunately,
    we should always keep the -0.0f here because:
    
    * The -0.0f is always the correct initial value.
    * We need to support the target that always honor signed zero.
    
    Thus, we need to leverage MODE_HAS_SIGNED_ZEROS when initialize
    instead of HONOR_SIGNED_ZEROS.  Then the target/backend can
    decide to honor the no-signed-zero or not.
    
    We also removed the testcase pr30957-1.c, as it makes undefined behavior
    whether the return value is positive or negative.
    
    The below tests are passed for this patch:
    
    * The riscv regression tests.
    * The aarch64 regression tests.
    * The x86 bootstrap and regression tests.
    
    gcc/ChangeLog:
    
            * loop-unroll.cc (insert_var_expansion_initialization): Leverage
            MODE_HAS_SIGNED_ZEROS for expansion variable initialization.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/pr30957-1.c: Remove.
    
    Signed-off-by: Pan Li <pan2.li@intel.com>

Diff:
---
 gcc/loop-unroll.cc               |  4 ++--
 gcc/testsuite/gcc.dg/pr30957-1.c | 36 ------------------------------------
 2 files changed, 2 insertions(+), 38 deletions(-)

diff --git a/gcc/loop-unroll.cc b/gcc/loop-unroll.cc
index 4176a21e308..bfdfe6c2bb7 100644
--- a/gcc/loop-unroll.cc
+++ b/gcc/loop-unroll.cc
@@ -1855,7 +1855,7 @@ insert_var_expansion_initialization (struct var_to_expand *ve,
   rtx var, zero_init;
   unsigned i;
   machine_mode mode = GET_MODE (ve->reg);
-  bool honor_signed_zero_p = HONOR_SIGNED_ZEROS (mode);
+  bool has_signed_zero_p = MODE_HAS_SIGNED_ZEROS (mode);
 
   if (ve->var_expansions.length () == 0)
     return;
@@ -1869,7 +1869,7 @@ insert_var_expansion_initialization (struct var_to_expand *ve,
     case MINUS:
       FOR_EACH_VEC_ELT (ve->var_expansions, i, var)
         {
-	  if (honor_signed_zero_p)
+	  if (has_signed_zero_p)
 	    zero_init = simplify_gen_unary (NEG, mode, CONST0_RTX (mode), mode);
 	  else
 	    zero_init = CONST0_RTX (mode);
diff --git a/gcc/testsuite/gcc.dg/pr30957-1.c b/gcc/testsuite/gcc.dg/pr30957-1.c
deleted file mode 100644
index 564410913ab..00000000000
--- a/gcc/testsuite/gcc.dg/pr30957-1.c
+++ /dev/null
@@ -1,36 +0,0 @@
-/* { dg-do run { xfail { mmix-*-* } } } */
-/* We don't (and don't want to) perform this optimisation on soft-float targets,
-   where each addition is a library call.  /
-/* { dg-require-effective-target hard_float } */
-/* -fassociative-math requires -fno-trapping-math and -fno-signed-zeros. */
-/* { dg-options "-O2 -funroll-loops -fassociative-math -fno-trapping-math -fno-signed-zeros -fvariable-expansion-in-unroller -fdump-rtl-loop2_unroll" } */
-
-extern void abort (void);
-extern void exit (int);
-
-float __attribute__((noinline))
-foo (float d, int n)
-{
-  unsigned i;
-  float accum = d;
-
-  for (i = 0; i < n; i++)
-    accum += d;
-
-  return accum;
-}
-
-int
-main ()
-{
-  /* When compiling standard compliant we expect foo to return -0.0.  But the
-     variable expansion during unrolling optimization (for this testcase enabled
-     by non-compliant -fassociative-math) instantiates copy(s) of the
-     accumulator which it initializes with +0.0.  Hence we expect that foo
-     returns +0.0.  */
-  if (__builtin_copysignf (1.0, foo (0.0 / -5.0, 10)) != 1.0)
-    abort ();
-  exit (0);
-}
-
-/* { dg-final { scan-rtl-dump "Expanding Accumulator" "loop2_unroll" { xfail mmix-*-* } } } */