[libclc] [libclc] Reduce bithacking in CLC frexp (PR #129871)

[Fraser Cormack via cfe-commits]

https://github.com/frasercrmck created https://github.com/llvm/llvm-project/pull/129871

Also replace some magic constants with named ones.

Checking against FP zero and using isnan and isinf functions allows the optimizer to create one unified @llvm.is.fpclass intrinsic. This results in fewer more canonical IR instructions.

>From 92a9ff3d37b64523577719c2be844061da1ac3ce Mon Sep 17 00:00:00 2001
From: Fraser Cormack <fraser at codeplay.com>
Date: Wed, 5 Mar 2025 11:20:21 +0000
Subject: [PATCH] [libclc] Reduce bithacking in CLC frexp

Also replace some magic constants with named ones.

Checking against FP zero and using isnan and isinf functions allows the
optimizer to create one unified @llvm.is.fpclass intrinsic. This results
in fewer more canonical IR instructions.
---
 libclc/clc/lib/generic/math/clc_frexp.cl  |  2 +
 libclc/clc/lib/generic/math/clc_frexp.inc | 52 +++++++++++++----------
 2 files changed, 32 insertions(+), 22 deletions(-)

diff --git a/libclc/clc/lib/generic/math/clc_frexp.cl b/libclc/clc/lib/generic/math/clc_frexp.cl
index ecc3eb6281b1e..dc9b00f7ef664 100644
--- a/libclc/clc/lib/generic/math/clc_frexp.cl
+++ b/libclc/clc/lib/generic/math/clc_frexp.cl
@@ -23,6 +23,8 @@
 #include <clc/clc_convert.h>
 #include <clc/internal/clc.h>
 #include <clc/math/math.h>
+#include <clc/relational/clc_isinf.h>
+#include <clc/relational/clc_isnan.h>
 #include <clc/relational/clc_select.h>
 #include <clc/utils.h>
 
diff --git a/libclc/clc/lib/generic/math/clc_frexp.inc b/libclc/clc/lib/generic/math/clc_frexp.inc
index 22966f08579a9..d59ccad9ac98c 100644
--- a/libclc/clc/lib/generic/math/clc_frexp.inc
+++ b/libclc/clc/lib/generic/math/clc_frexp.inc
@@ -28,17 +28,22 @@
 _CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE
 __clc_frexp(__CLC_GENTYPE x, __CLC_ADDRESS_SPACE __CLC_INTN *ep) {
   __CLC_INTN i = __CLC_AS_INTN(x);
-  __CLC_INTN ai = i & 0x7fffffff;
-  __CLC_INTN d = ai > 0 & ai < 0x00800000;
-  /* scale subnormal by 2^26 without multiplying */
+  __CLC_INTN ai = i & EXSIGNBIT_SP32;
+
+  // Scale subnormal by 2^26 without multiplying
+  __CLC_INTN is_subnormal = ai > 0 && ai < 0x00800000;
   __CLC_GENTYPE s = __CLC_AS_GENTYPE(ai | 0x0d800000) - 0x1.0p-100f;
-  ai = __clc_select(ai, __CLC_AS_INTN(s), d);
-  __CLC_INTN e =
-      (ai >> 23) - 126 - __clc_select((__CLC_INTN)0, (__CLC_INTN)26, d);
-  __CLC_INTN t = ai == (__CLC_INTN)0 | e == (__CLC_INTN)129;
-  i = (i & (__CLC_INTN)0x80000000) | (__CLC_INTN)0x3f000000 | (ai & 0x007fffff);
-  *ep = __clc_select(e, (__CLC_INTN)0, t);
-  return __clc_select(__CLC_AS_GENTYPE(i), x, t);
+  ai = __clc_select(ai, __CLC_AS_INTN(s), is_subnormal);
+  __CLC_INTN e = (ai >> EXPSHIFTBITS_SP32) - 126 -
+                 __clc_select((__CLC_INTN)0, (__CLC_INTN)26, is_subnormal);
+
+  i = (i & (__CLC_INTN)SIGNBIT_SP32) | (__CLC_INTN)HALFEXPBITS_SP32 |
+      (ai & (__CLC_INTN)MANTBITS_SP32);
+
+  __CLC_INTN is_inf_nan_or_zero =
+      x == __CLC_FP_LIT(0.0) || __clc_isinf(x) || __clc_isnan(x);
+  *ep = __clc_select(e, (__CLC_INTN)0, is_inf_nan_or_zero);
+  return __clc_select(__CLC_AS_GENTYPE(i), x, is_inf_nan_or_zero);
 }
 #endif
 
@@ -56,19 +61,22 @@ __clc_frexp(__CLC_GENTYPE x, __CLC_ADDRESS_SPACE __CLC_INTN *ep) {
 _CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE
 __clc_frexp(__CLC_GENTYPE x, __CLC_ADDRESS_SPACE __CLC_INTN *ep) {
   __CLC_LONGN i = __CLC_AS_LONGN(x);
-  __CLC_LONGN ai = i & 0x7fffffffffffffffL;
-  __CLC_LONGN d = ai > 0 & ai < 0x0010000000000000L;
-  // scale subnormal by 2^54 without multiplying
+  __CLC_LONGN ai = i & EXSIGNBIT_DP64;
+
+  // Scale subnormal by 2^54 without multiplying
+  __CLC_LONGN is_subnormal = ai > 0 && ai < 0x0010000000000000L;
   __CLC_GENTYPE s = __CLC_AS_GENTYPE(ai | 0x0370000000000000L) - 0x1.0p-968;
-  ai = __clc_select(ai, __CLC_AS_LONGN(s), d);
-  __CLC_LONGN e = (ai >> 52) - (__CLC_LONGN)1022 -
-                  __clc_select((__CLC_LONGN)0, (__CLC_LONGN)54, d);
-  __CLC_LONGN t = ai == 0 | e == 1025;
-  i = (i & (__CLC_LONGN)0x8000000000000000L) |
-      (__CLC_LONGN)0x3fe0000000000000L |
-      (ai & (__CLC_LONGN)0x000fffffffffffffL);
-  *ep = __CLC_CONVERT_INTN(__clc_select(e, 0L, t));
-  return __clc_select(__CLC_AS_GENTYPE(i), x, t);
+  ai = __clc_select(ai, __CLC_AS_LONGN(s), is_subnormal);
+  __CLC_LONGN e = (ai >> EXPSHIFTBITS_DP64) - (__CLC_LONGN)1022 -
+                  __clc_select((__CLC_LONGN)0, (__CLC_LONGN)54, is_subnormal);
+
+  i = (i & (__CLC_LONGN)SIGNBIT_DP64) | (__CLC_LONGN)HALFEXPBITS_DP64 |
+      (ai & (__CLC_LONGN)MANTBITS_DP64);
+
+  __CLC_LONGN is_inf_nan_or_zero =
+      x == __CLC_FP_LIT(0.0) || __clc_isinf(x) || __clc_isnan(x);
+  *ep = __CLC_CONVERT_INTN(__clc_select(e, 0L, is_inf_nan_or_zero));
+  return __clc_select(__CLC_AS_GENTYPE(i), x, is_inf_nan_or_zero);
 }
 
 #endif