[builtins] Add support for single-precision-only-FPU ARM targets.

[chaosdefinition]

Summary

This patch enables building compiler-rt builtins for ARM targets that only support single-precision floating point instructions (e.g., those with -mfpu=fpv4-sp-d16).

This fixes PR42838.

[psmith]

This looks good to me. The __ARM_FP feature test macro is defined in the ACLE and 0x8 is the right flag to check for Double precision support. I've tested at least one single precision only build.

I suggest waiting a day or two before committing to see if anyone else has any objections or alternative implementation suggestions.

[chaosdefinition]

@psmith Thank you for reviewing! I'll wait a few days for other comments.

[chaosdefinition]

If there are no more comments, can someone please commit this for me? I don't have commit access to LLVM.

[psmith]

In D90698#2389872, @chaosdefinition wrote:

If there are no more comments, can someone please commit this for me? I don't have commit access to LLVM.

That's a little complicated for me as I need to go through various internal company procedures to commit something I didn't write. I can do this but it will take time, if there are any others that can do it faster then please do.

[psmith]

Now committed. Commit message has your name and email address.

[psmith]

Assuming there are no problems with the bots or other downstream builds, please update the PR with a link to this review.

[chaosdefinition]

In D90698#2390693, @psmith wrote:

In D90698#2389872, @chaosdefinition wrote:

If there are no more comments, can someone please commit this for me? I don't have commit access to LLVM.

That's a little complicated for me as I need to go through various internal company procedures to commit something I didn't write. I can do this but it will take time, if there are any others that can do it faster then please do.

Thank you for taking time doing this! I'll consider getting myself commit access for future patches.

compiler-rt/lib/builtins/CMakeLists.txt

set(arm_Thumb1_JT_SOURCES
   arm/switch32.S
   arm/switch8.S
   arm/switchu8.S
 )
 set(arm_Thumb1_SjLj_EH_SOURCES
   arm/restore_vfp_d8_d15_regs.S
   arm/save_vfp_d8_d15_regs.S
 )
-set(arm_Thumb1_VFPv2_SOURCES
+set(arm_Thumb1_VFPv2_DP_SOURCES
   arm/adddf3vfp.S
-  arm/addsf3vfp.S
   arm/divdf3vfp.S
-  arm/divsf3vfp.S
   arm/eqdf2vfp.S
-  arm/eqsf2vfp.S
   arm/extendsfdf2vfp.S
   arm/fixdfsivfp.S
-  arm/fixsfsivfp.S
   arm/fixunsdfsivfp.S
-  arm/fixunssfsivfp.S
   arm/floatsidfvfp.S
-  arm/floatsisfvfp.S
   arm/floatunssidfvfp.S
-  arm/floatunssisfvfp.S
   arm/gedf2vfp.S
-  arm/gesf2vfp.S
   arm/gtdf2vfp.S
-  arm/gtsf2vfp.S
   arm/ledf2vfp.S
-  arm/lesf2vfp.S
   arm/ltdf2vfp.S
-  arm/ltsf2vfp.S
   arm/muldf3vfp.S
-  arm/mulsf3vfp.S
   arm/nedf2vfp.S
   arm/negdf2vfp.S
-  arm/negsf2vfp.S
-  arm/nesf2vfp.S
   arm/subdf3vfp.S
-  arm/subsf3vfp.S
   arm/truncdfsf2vfp.S
   arm/unorddf2vfp.S
+)
+set(arm_Thumb1_VFPv2_SP_SOURCES
+  arm/addsf3vfp.S
+  arm/divsf3vfp.S
+  arm/eqsf2vfp.S
+  arm/fixsfsivfp.S
+  arm/fixunssfsivfp.S
+  arm/floatsisfvfp.S
+  arm/floatunssisfvfp.S
+  arm/gesf2vfp.S
+  arm/gtsf2vfp.S
+  arm/lesf2vfp.S
+  arm/ltsf2vfp.S
+  arm/mulsf3vfp.S
+  arm/negsf2vfp.S
+  arm/nesf2vfp.S
+  arm/subsf3vfp.S
   arm/unordsf2vfp.S
 )
 set(arm_Thumb1_icache_SOURCES
   arm/sync_synchronize.S
 )
 set(arm_Thumb1_SOURCES
   ${arm_Thumb1_JT_SOURCES}
   ${arm_Thumb1_SjLj_EH_SOURCES}
-  ${arm_Thumb1_VFPv2_SOURCES}
+  ${arm_Thumb1_VFPv2_DP_SOURCES}
+  ${arm_Thumb1_VFPv2_SP_SOURCES}
   ${arm_Thumb1_icache_SOURCES}
 )
 
 if(MINGW)
   set(arm_SOURCES
     arm/aeabi_idivmod.S
     arm/aeabi_ldivmod.S
     arm/aeabi_uidivmod.S
else ()
 
   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
     if (CAN_TARGET_${arch})
       # For ARM archs, exclude any VFP builtins if VFP is not supported
       if (${arch} MATCHES "^(arm|armhf|armv7|armv7s|armv7k|armv7m|armv7em)$")
         string(REPLACE ";" " " _TARGET_${arch}_CFLAGS "${TARGET_${arch}_CFLAGS}")
         check_compile_definition(__VFP_FP__ "${CMAKE_C_FLAGS} ${_TARGET_${arch}_CFLAGS}" COMPILER_RT_HAS_${arch}_VFP)
         if(NOT COMPILER_RT_HAS_${arch}_VFP)
-          list(REMOVE_ITEM ${arch}_SOURCES ${arm_Thumb1_VFPv2_SOURCES} ${arm_Thumb1_SjLj_EH_SOURCES})
+          list(REMOVE_ITEM ${arch}_SOURCES ${arm_Thumb1_VFPv2_DP_SOURCES} ${arm_Thumb1_VFPv2_SP_SOURCES} ${arm_Thumb1_SjLj_EH_SOURCES})
+        else()
+          # Exclude any double-precision builtins if VFP is single-precision-only
+          check_c_source_compiles("#if !(__ARM_FP & 0x8)
+                                   #error No double-precision support!
+                                   #endif
+                                   int main() { return 0; }" COMPILER_RT_HAS_${arch}_VFP_DP)
+          if(NOT COMPILER_RT_HAS_${arch}_VFP_DP)
+            list(REMOVE_ITEM ${arch}_SOURCES ${arm_Thumb1_VFPv2_DP_SOURCES})
+          endif()
         endif()
       endif()
 
       # Remove a generic C builtin when an arch-specific builtin is specified.
       filter_builtin_sources(${arch}_SOURCES ${arch})
 
       # Needed for clear_cache on debug mode, due to r7's usage in inline asm.
       # Release mode already sets it via -O2/3, Debug mode doesn't.