[compiler-rt] [RISCV][compiler-rt] Small fixes for __riscv_feature_bits (PR #99958)

[Philip Reames via llvm-commits]

https://github.com/preames updated https://github.com/llvm/llvm-project/pull/99958

>From 1e6f521b25ff60432c4c6ead08e9c6e473977b07 Mon Sep 17 00:00:00 2001
From: Philip Reames <preames at rivosinc.com>
Date: Mon, 22 Jul 2024 14:51:55 -0700
Subject: [PATCH 1/4] [RISCV][compiler-rt] Small fixes for __riscv_feature_bits

Changes included:
* Adding CONSTRUCTOR_ATTRIBUTE so that the static data is setup early on
  in process lifetime.  This is required by gcc docs for
  __builtin_cpu_supports which we hope to implement in terms of this.
* Move the length initialization outside of the #if defined(__linux__)
  block so that the length field always reflects the size of the structures
  even if non of the feature bits are non-zero.
* Change the __riscv_vendor_feature_bits.length field to match the length
  of the actual structure.

Note that this change has not been built or tested.  I could not figure
out how to get a working cross build for compiler-rt setup.
---
 compiler-rt/lib/builtins/riscv/feature_bits.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/compiler-rt/lib/builtins/riscv/feature_bits.c b/compiler-rt/lib/builtins/riscv/feature_bits.c
index 77422935bd2d3..da4208396a0f9 100644
--- a/compiler-rt/lib/builtins/riscv/feature_bits.c
+++ b/compiler-rt/lib/builtins/riscv/feature_bits.c
@@ -204,12 +204,10 @@ static void initRISCVFeature(struct riscv_hwprobe Hwprobes[]) {
   // This unsets all extension bitmask bits.
 
   // Init vendor extension
-  __riscv_vendor_feature_bits.length = 0;
   __riscv_vendor_feature_bits.vendorID = Hwprobes[2].value;
 
   // Init standard extension
   // TODO: Maybe Extension implied generate from tablegen?
-  __riscv_feature_bits.length = RISCV_FEATURE_BITS_LENGTH;
 
   unsigned long long features[RISCV_FEATURE_BITS_LENGTH];
   int i;
@@ -277,11 +275,21 @@ static void initRISCVFeature(struct riscv_hwprobe Hwprobes[]) {
 
 static int FeaturesBitCached = 0;
 
-void __init_riscv_feature_bits() {
+void __init_riscv_feature_bits() CONSTRUCTOR_ATTRIBUTE;
+
+// A constructor function that is sets __riscv_feature_bits, and
+// __riscv_vendor_feature_bits to the right values.  This needs to run
+// only once.  This constructor is given the highest priority and it should
+// run before constructors without the priority set.  However, it still runs
+// after ifunc initializers and needs to be called explicitly there.
+void CONSTRUCTOR_ATTRIBUTE __init_riscv_feature_bits() {
 
   if (FeaturesBitCached)
     return;
 
+  __riscv_feature_bits.length = RISCV_FEATURE_BITS_LENGTH;
+  __riscv_vendor_feature_bits.length = RISCV_VENDOR_FEATURE_BITS_LENGTH;
+
 #if defined(__linux__)
   struct riscv_hwprobe Hwprobes[] = {
       {RISCV_HWPROBE_KEY_BASE_BEHAVIOR, 0},

>From 90292050675dde99ff3072e4729bb3d20cb6a603 Mon Sep 17 00:00:00 2001
From: Philip Reames <preames at rivosinc.com>
Date: Mon, 22 Jul 2024 19:32:53 -0700
Subject: [PATCH 2/4] Address review comment

---
 compiler-rt/lib/builtins/riscv/feature_bits.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler-rt/lib/builtins/riscv/feature_bits.c b/compiler-rt/lib/builtins/riscv/feature_bits.c
index da4208396a0f9..759555aaac882 100644
--- a/compiler-rt/lib/builtins/riscv/feature_bits.c
+++ b/compiler-rt/lib/builtins/riscv/feature_bits.c
@@ -277,7 +277,7 @@ static int FeaturesBitCached = 0;
 
 void __init_riscv_feature_bits() CONSTRUCTOR_ATTRIBUTE;
 
-// A constructor function that is sets __riscv_feature_bits, and
+// A constructor function that sets __riscv_feature_bits, and
 // __riscv_vendor_feature_bits to the right values.  This needs to run
 // only once.  This constructor is given the highest priority and it should
 // run before constructors without the priority set.  However, it still runs

>From 4d589a348665e16e12900cb43bc4ff8da1a6c652 Mon Sep 17 00:00:00 2001
From: Philip Reames <preames at rivosinc.com>
Date: Mon, 22 Jul 2024 19:37:21 -0700
Subject: [PATCH 3/4] Attempt to fix build

---
 compiler-rt/lib/builtins/riscv/feature_bits.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/compiler-rt/lib/builtins/riscv/feature_bits.c b/compiler-rt/lib/builtins/riscv/feature_bits.c
index 759555aaac882..946208fbb8bf1 100644
--- a/compiler-rt/lib/builtins/riscv/feature_bits.c
+++ b/compiler-rt/lib/builtins/riscv/feature_bits.c
@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "cpu_model.h"
+
 #define RISCV_FEATURE_BITS_LENGTH 1
 struct {
   unsigned length;

>From ede49c7485fa49ab0b73707ed02b152afc95dfcd Mon Sep 17 00:00:00 2001
From: Philip Reames <preames at rivosinc.com>
Date: Tue, 23 Jul 2024 09:16:20 -0700
Subject: [PATCH 4/4] Move feature_bits.c into cpu_model

Patch by @BeMG
---
 compiler-rt/lib/builtins/CMakeLists.txt                         | 2 +-
 .../lib/builtins/{riscv/feature_bits.c => cpu_model/riscv.c}    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)
 rename compiler-rt/lib/builtins/{riscv/feature_bits.c => cpu_model/riscv.c} (99%)

diff --git a/compiler-rt/lib/builtins/CMakeLists.txt b/compiler-rt/lib/builtins/CMakeLists.txt
index 88a5998fd4610..13adbd6c4d57d 100644
--- a/compiler-rt/lib/builtins/CMakeLists.txt
+++ b/compiler-rt/lib/builtins/CMakeLists.txt
@@ -739,7 +739,7 @@ endif()
 set(powerpc64le_SOURCES ${powerpc64_SOURCES})
 
 set(riscv_SOURCES
-  riscv/feature_bits.c
+  cpu_model/riscv.c
   riscv/fp_mode.c
   riscv/save.S
   riscv/restore.S
diff --git a/compiler-rt/lib/builtins/riscv/feature_bits.c b/compiler-rt/lib/builtins/cpu_model/riscv.c
similarity index 99%
rename from compiler-rt/lib/builtins/riscv/feature_bits.c
rename to compiler-rt/lib/builtins/cpu_model/riscv.c
index 946208fbb8bf1..145954e704433 100644
--- a/compiler-rt/lib/builtins/riscv/feature_bits.c
+++ b/compiler-rt/lib/builtins/cpu_model/riscv.c
@@ -1,4 +1,4 @@
-//=== feature_bits.c - Update RISC-V Feature Bits Structure -*- C -*-=========//
+//=== cpu_model/riscv.c - Update RISC-V Feature Bits Structure -*- C -*-======//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.