[llvm] Enable logf128 constant folding for AArch64 (PR #96287)

[Matthew Devereau via llvm-commits]

https://github.com/MDevereau updated https://github.com/llvm/llvm-project/pull/96287

>From 4cc6905d7020140bf1facad3ad9c0888cb7e4734 Mon Sep 17 00:00:00 2001
From: Matt Devereau <matthew.devereau at arm.com>
Date: Fri, 21 Jun 2024 08:34:04 +0000
Subject: [PATCH 1/3] Enable logf128 constant folding for AArch64

AArch64 has a long double bit length of 128. Therefore, it can benefit
from constant fp128 folding. GCC versions more recent than version 12
must use the _Float128 type for logf128.
---
 llvm/include/llvm/Support/float128.h  | 9 ++++++++-
 llvm/lib/Analysis/ConstantFolding.cpp | 4 ++--
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/llvm/include/llvm/Support/float128.h b/llvm/include/llvm/Support/float128.h
index e15a98dc5a677..f1931c145f0fc 100644
--- a/llvm/include/llvm/Support/float128.h
+++ b/llvm/include/llvm/Support/float128.h
@@ -11,7 +11,14 @@
 
 namespace llvm {
 
-#if defined(__clang__) && defined(__FLOAT128__) &&                             \
+#if defined(__aarch64__)
+#define HAS_IEE754_FLOAT128
+#if (defined(__GNUC__) && __GNUC__ > 12)
+typedef _Float128 float128;
+#else
+typedef long double float128;
+#endif
+#elif defined(__clang__) && defined(__FLOAT128__) &&                           \
     defined(__SIZEOF_INT128__) && !defined(__LONG_DOUBLE_IBM128__)
 #define HAS_IEE754_FLOAT128
 typedef __float128 float128;
diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 512d1aadd5346..4329d2e9a0556 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -1784,8 +1784,8 @@ Constant *ConstantFoldFP(double (*NativeFP)(double), const APFloat &V,
 }
 
 #if defined(HAS_IEE754_FLOAT128) && defined(HAS_LOGF128)
-Constant *ConstantFoldFP128(long double (*NativeFP)(long double),
-                            const APFloat &V, Type *Ty) {
+Constant *ConstantFoldFP128(float128 (*NativeFP)(float128), const APFloat &V,
+                            Type *Ty) {
   llvm_fenv_clearexcept();
   float128 Result = NativeFP(V.convertToQuad());
   if (llvm_fenv_testexcept()) {

>From 97a0b2005dc477c491b942933f5ecae7acf187e8 Mon Sep 17 00:00:00 2001
From: Matt Devereau <matthew.devereau at arm.com>
Date: Wed, 26 Jun 2024 13:57:59 +0000
Subject: [PATCH 2/3] Remove aarch64 constraint

Also enable optimisation without cmake opt-in
---
 llvm/include/llvm/Support/float128.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/Support/float128.h b/llvm/include/llvm/Support/float128.h
index f1931c145f0fc..6068c556ca616 100644
--- a/llvm/include/llvm/Support/float128.h
+++ b/llvm/include/llvm/Support/float128.h
@@ -11,7 +11,8 @@
 
 namespace llvm {
 
-#if defined(__aarch64__)
+#if !defined(__LONG_DOUBLE_IBM128__) && (__SIZEOF_LONG_DOUBLE__ == 16) &&      \
+    (__SIZEOF_INT128__ == 16) && (__LDBL_MANT_DIG__ == 113)
 #define HAS_IEE754_FLOAT128
 #if (defined(__GNUC__) && __GNUC__ > 12)
 typedef _Float128 float128;

>From 94c6914a6048c8f044bbe573539f81d7fd9dfecf Mon Sep 17 00:00:00 2001
From: Matt Devereau <matthew.devereau at arm.com>
Date: Wed, 26 Jun 2024 15:08:10 +0000
Subject: [PATCH 3/3] Enable optimization without opt-in

---
 llvm/cmake/config-ix.cmake | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/llvm/cmake/config-ix.cmake b/llvm/cmake/config-ix.cmake
index 0aae13e30f2ab..7b092917a1bb8 100644
--- a/llvm/cmake/config-ix.cmake
+++ b/llvm/cmake/config-ix.cmake
@@ -247,17 +247,6 @@ else()
   set(HAVE_LIBEDIT 0)
 endif()
 
-if(LLVM_HAS_LOGF128)
-  include(CheckCXXSymbolExists)
-  check_cxx_symbol_exists(logf128 math.h HAS_LOGF128)
-
-  if(LLVM_HAS_LOGF128 STREQUAL FORCE_ON AND NOT HAS_LOGF128)
-    message(FATAL_ERROR "Failed to configure logf128")
-  endif()
-
-  set(LLVM_HAS_LOGF128 "${HAS_LOGF128}")
-endif()
-
 # function checks
 check_symbol_exists(arc4random "stdlib.h" HAVE_DECL_ARC4RANDOM)
 find_package(Backtrace)
@@ -271,6 +260,8 @@ if(C_SUPPORTS_WERROR_UNGUARDED_AVAILABILITY_NEW)
   set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -Werror=unguarded-availability-new")
 endif()
 
+check_function_exists(logf128 math.h HAS_LOGF128)
+
 # Determine whether we can register EH tables.
 check_symbol_exists(__register_frame "${CMAKE_CURRENT_LIST_DIR}/unwind.h" HAVE_REGISTER_FRAME)
 check_symbol_exists(__deregister_frame "${CMAKE_CURRENT_LIST_DIR}/unwind.h" HAVE_DEREGISTER_FRAME)