Configure SwissTable to target older processors

On Intel and compatibles, SwissTable can benefit from SSE2 and SSSE3 if
available. Currently, though, it determines availability through a
compile-time check, which pins binary packages to the CPU of the
builder. Correct this:

  - Disable SSE2 and SSSE3 on i386. SSSE3 has never been available on
    i386 CPUs, and Debian supports some i386 CPUs that lack the
    extension (e.g., the Athlon XP).

  - Disable SSSE3 on amd64. SSSE3 did not appear until the mid-'00s,
    and Debian supports all amd64 CPUs, even going back to the original
    Opteron. Keep SSE2 enabled, since all amd64 CPUs support SSE2.

2 files changed, 40 insertions, 5 deletions

diff --git a/debian/changelog b/debian/changelog
index 9a778cd0..6aaaaef4 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -2,6 +2,8 @@ abseil (0~20200225.2-2) UNRELEASED; urgency=medium
 
   * Rebuild for unstable.
   * Rework symbols file using pkg-kde-tools for increased robustness.
+  * Avoid SSSE3 on amd64 and SSE2 on i386 for greater processor
+    compatibility.
 
  -- Benjamin Barenblat <bbaren@debian.org>  Thu, 23 Jul 2020 10:53:19 -0400
 
diff --git a/debian/patches/configure.diff b/debian/patches/configure.diff
index fd29fa59..bb88ae7d 100644
--- a/debian/patches/configure.diff
+++ b/debian/patches/configure.diff
@@ -11,6 +11,13 @@ Configure Abseil for Debian.
     (rather than aliases for the std:: versions), and compile everything in an
     inline namespace.
 
+  - Disable Intel SSE2 on i386, since Debian supports some i386 processors
+    without that extension. Keep it enabled on amd64, since all amd64 processors
+    have it.
+
+  - Disable Intel SSSE3 entirely, since no i386 processor supports it and Debian
+    supports amd64 processors without it.
+
 --- a/CMake/AbseilHelpers.cmake
 +++ b/CMake/AbseilHelpers.cmake
 @@ -215,6 +215,9 @@
@@ -25,7 +32,7 @@ Configure Abseil for Debian.
      add_library(${_NAME} INTERFACE)
 --- a/absl/base/options.h
 +++ b/absl/base/options.h
-@@ -100,7 +100,7 @@ ABSL_OPTION_USE_STD_ANY
+@@ -100,7 +100,7 @@
  // User code should not inspect this macro.  To check in the preprocessor if
  // absl::any is a typedef of std::any, use the feature macro ABSL_USES_STD_ANY.
  
@@ -34,7 +41,7 @@ Configure Abseil for Debian.
  
  
  // ABSL_OPTION_USE_STD_OPTIONAL
-@@ -127,7 +127,7 @@ ABSL_OPTION_USE_STD_OPTIONAL
+@@ -127,7 +127,7 @@
  // absl::optional is a typedef of std::optional, use the feature macro
  // ABSL_USES_STD_OPTIONAL.
  
@@ -43,7 +50,7 @@ Configure Abseil for Debian.
  
  
  // ABSL_OPTION_USE_STD_STRING_VIEW
-@@ -154,7 +154,7 @@ ABSL_OPTION_USE_STD_STRING_VIEW
+@@ -154,7 +154,7 @@
  // absl::string_view is a typedef of std::string_view, use the feature macro
  // ABSL_USES_STD_STRING_VIEW.
  
@@ -52,7 +59,7 @@ Configure Abseil for Debian.
  
  // ABSL_OPTION_USE_STD_VARIANT
  //
-@@ -180,7 +180,7 @@ ABSL_OPTION_USE_STD_VARIANT
+@@ -180,7 +180,7 @@
  // absl::variant is a typedef of std::variant, use the feature macro
  // ABSL_USES_STD_VARIANT.
  
@@ -61,7 +68,7 @@ Configure Abseil for Debian.
  
  
  // ABSL_OPTION_USE_INLINE_NAMESPACE
-@@ -206,6 +206,6 @@ ABSL_OPTION_INLINE_NAMESPACE_NAME
+@@ -206,6 +206,6 @@
  // allowed.
  
  #define ABSL_OPTION_USE_INLINE_NAMESPACE 1
@@ -69,3 +76,29 @@ Configure Abseil for Debian.
 +#define ABSL_OPTION_INLINE_NAMESPACE_NAME debian0
  
  #endif  // ABSL_BASE_OPTIONS_H_
+--- a/absl/container/internal/have_sse.h
++++ b/absl/container/internal/have_sse.h
+@@ -17,22 +17,14 @@
+ #define ABSL_CONTAINER_INTERNAL_HAVE_SSE_H_
+ 
+ #ifndef SWISSTABLE_HAVE_SSE2
+-#if defined(__SSE2__) ||  \
+-    (defined(_MSC_VER) && \
+-     (defined(_M_X64) || (defined(_M_IX86) && _M_IX86_FP >= 2)))
++#if defined(__x86_64__) || (defined(_MSC_VER) && defined(_M_X64))
+ #define SWISSTABLE_HAVE_SSE2 1
+ #else
+ #define SWISSTABLE_HAVE_SSE2 0
+ #endif
+ #endif
+ 
+-#ifndef SWISSTABLE_HAVE_SSSE3
+-#ifdef __SSSE3__
+-#define SWISSTABLE_HAVE_SSSE3 1
+-#else
+ #define SWISSTABLE_HAVE_SSSE3 0
+-#endif
+-#endif
+ 
+ #if SWISSTABLE_HAVE_SSSE3 && !SWISSTABLE_HAVE_SSE2
+ #error "Bad configuration!"