[gcc r17-2330] rs6000: Add -mdense-math option

https://gcc.gnu.org/g:2601cb4d27364e2ae5c0eb4f53e186e0e0ecadde

commit r17-2330-g2601cb4d27364e2ae5c0eb4f53e186e0e0ecadde
Author: Surya Kumari Jangala <[email protected]>
Date:   Thu Jul 9 03:46:23 2026 -0500

    rs6000: Add -mdense-math option
    
    Add the -mdense-math/-mno-dense-math compiler option to control emission
    of Dense Math Facility (DMF) instructions.  The option is backed by
    OPTION_MASK_DMF and exposes a TARGET_DMF macro for use throughout the
    backend.
    
    When -mcpu=future is specified and -mdense-math is not mentioned
    explicitly, DMF is enabled automatically.  Explicitly requesting
    -mdense-math on a non-future target is a hard error.
    
    2026-07-09  Surya Kumari Jangala  <[email protected]>
    
    gcc:
            * config/rs6000/rs6000-cpus.def (FUTURE_MASKS_SERVER): Add OPTION_MASK_DMF.
            (POWERPC_MASKS): Likewise.
            * config/rs6000/rs6000.cc (rs6000_option_override_internal): Enable
            OPTION_MASK_DMF by default when TARGET_FUTURE is set and the
            flag was not explicitly given; emit an error and clear the flag
            when -mdense-math is requested on a non-future target.
            (rs6000_opt_masks): Add "dense-math" entry for OPTION_MASK_DMF.
            * config/rs6000/rs6000.opt (mdense-math): New option backed by Mask(DMF).
            * doc/invoke.texi: Add -mdense-math.

Diff:
---
 gcc/config/rs6000/rs6000-cpus.def |  4 +++-
 gcc/config/rs6000/rs6000.cc       | 14 ++++++++++++++
 gcc/config/rs6000/rs6000.opt      |  4 ++++
 gcc/doc/invoke.texi               | 12 ++++++++++--
 4 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/gcc/config/rs6000/rs6000-cpus.def b/gcc/config/rs6000/rs6000-cpus.def
index a110860acce6..365e0c6899c1 100644
--- a/gcc/config/rs6000/rs6000-cpus.def
+++ b/gcc/config/rs6000/rs6000-cpus.def
@@ -85,7 +85,8 @@
 
 /* -mcpu=future flags.  */
 #define FUTURE_MASKS_SERVER	(POWER11_MASKS_SERVER			\
-				 | OPTION_MASK_FUTURE)
+				 | OPTION_MASK_FUTURE			\
+				 | OPTION_MASK_DMF)
 
 /* Flags that need to be turned off if -mno-vsx.  */
 #define OTHER_VSX_VECTOR_MASKS	(OPTION_MASK_EFFICIENT_UNALIGNED_VSX	\
@@ -126,6 +127,7 @@
 				 | OPTION_MASK_POWER10			\
 				 | OPTION_MASK_POWER11			\
 				 | OPTION_MASK_FUTURE			\
+				 | OPTION_MASK_DMF			\
 				 | OPTION_MASK_P10_FUSION		\
 				 | OPTION_MASK_HTM			\
 				 | OPTION_MASK_ISEL			\
diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index d8669d9ffce4..7743c9cdc4a1 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -4381,6 +4381,19 @@ rs6000_option_override_internal (bool global_init_p)
       rs6000_isa_flags &= ~OPTION_MASK_MMA;
     }
 
+  /* Enable -mdense_math by default on future systems.  */
+  if (TARGET_FUTURE && (rs6000_isa_flags_explicit & OPTION_MASK_DMF) == 0)
+    rs6000_isa_flags |= OPTION_MASK_DMF;
+
+  /* Turn off DMF options on non-future systems.  */
+  else if (!TARGET_FUTURE && TARGET_DMF)
+    {
+      if ((rs6000_isa_flags_explicit & OPTION_MASK_DMF) != 0)
+	error ("%qs requires %qs", "-mdense_math", "-mcpu=future");
+
+      rs6000_isa_flags &= ~OPTION_MASK_DMF;
+    }
+
   /* Enable power10 fusion if we are tuning for power10, even if we aren't
      generating power10 instructions.  */
   if (!(rs6000_isa_flags_explicit & OPTION_MASK_P10_FUSION))
@@ -24470,6 +24483,7 @@ static struct rs6000_opt_mask const rs6000_opt_masks[] =
   { "power10",			OPTION_MASK_POWER10,		false, true  },
   { "power11",			OPTION_MASK_POWER11,		false, false },
   { "future",			OPTION_MASK_FUTURE,		false, false },
+  { "dense-math",		OPTION_MASK_DMF,		false, true  },
   { "hard-dfp",			OPTION_MASK_DFP,		false, true  },
   { "htm",			OPTION_MASK_HTM,		false, true  },
   { "isel",			OPTION_MASK_ISEL,		false, true  },
diff --git a/gcc/config/rs6000/rs6000.opt b/gcc/config/rs6000/rs6000.opt
index 2b6ec5222fc1..d9e9de92b21a 100644
--- a/gcc/config/rs6000/rs6000.opt
+++ b/gcc/config/rs6000/rs6000.opt
@@ -599,6 +599,10 @@ Target Undocumented Mask(POWER11) Var(rs6000_isa_flags) WarnRemoved
 mfuture
 Target Undocumented Mask(FUTURE) Var(rs6000_isa_flags) Warn(Do not use %<-mfuture>, use %<-mcpu=future>)
 
+mdense-math
+Target Mask(DMF) Var(rs6000_isa_flags)
+Generate (do not generate) DMF (Dense Math Facility) instructions.
+
 mprefixed
 Target Mask(PREFIXED) Var(rs6000_isa_flags)
 Generate (do not generate) prefixed memory instructions.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 354ceb76f538..3234efa04ba2 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -1407,7 +1407,7 @@ See RS/6000 and PowerPC Options.
 -mgnu-attribute
 -mstack-protector-guard=@var{guard}  -mstack-protector-guard-reg=@var{reg}
 -mstack-protector-guard-offset=@var{offset}  -mprefixed
--mpcrel  -mmma  -mrop-protect  -mprivileged
+-mpcrel  -mmma  -mdense-math  -mrop-protect  -mprivileged
 -mno-splat-word-constant  -mno-splat-float-constant
 -mno-ieee128-constant  -mno-warn-altivec-long}
 
@@ -31792,7 +31792,7 @@ following options:
 -mcrypto  -mhtm  -mpower8-fusion
 -mquad-memory  -mquad-memory-atomic  -mfloat128
 -mfloat128-hardware  -mprefixed  -mpcrel  -mmma
--mrop-protect}
+-mdense-math -mrop-protect}
 
 The particular options set for any particular CPU varies between
 compiler versions, depending on what setting seems to produce optimal
@@ -32889,6 +32889,14 @@ Generate (do not generate) the MMA instructions.  The @option{-mma}
 option requires that the option @option{-mcpu=power10} (or later)
 is enabled.
 
+@opindex mdense-math
+@opindex mno-dense-math
+@item -mdense-math
+@itemx -mno-dense-math
+Generate (do not generate) Dense Math Facility (DMF) instructions.
+The @option{-mdense-math} option requires that the option
+@option{-mcpu=future} (or later) is enabled.
+
 @opindex mrop-protect
 @opindex mno-rop-protect
 @item -mrop-protect