[ARM] Emit ABI_FP_rounding attribute.

[• chatur01]

Summary

LLVM understands a -enable-sign-dependent-rounding-fp-math codegen option. When the user has specified this option, the Tag_ABI_FP_rounding attribute should be emitted with value 1. This option currently does not appear to disable transformations and optimizations that assume default floating point rounding behavior, AFAICT, but the intention should be recorded in the build attributes, regardless of what the compiler actually does with the intention.

Aside: when Clang supports -frounding-math, it will be using this LLVM option in the translation IIUC. The -frounding-math is what toggles this build attribute.

[t.p.northover]

Hi Charlie,

This looks fine to me.

Cheers.

Tim.

[• chatur01]

Thanks Tim! Committed as r223218.

lib/Target/ARM/ARMAsmPrinter.cpp

   }
 
   // Signal various FP modes.
   if (!TM.Options.UnsafeFPMath) {
     ATS.emitAttribute(ARMBuildAttrs::ABI_FP_denormal,
                       ARMBuildAttrs::IEEEDenormals);
     ATS.emitAttribute(ARMBuildAttrs::ABI_FP_exceptions,
                       ARMBuildAttrs::Allowed);
+
+    // If the user has permitted this code to choose the IEEE 754
+    // rounding at run-time, emit the rounding attribute.
+    if (TM.Options.HonorSignDependentRoundingFPMathOption)
+      ATS.emitAttribute(ARMBuildAttrs::ABI_FP_rounding,
+                        ARMBuildAttrs::Allowed);
   } else {
     if (!Subtarget->hasVFP2()) {
       // When the target doesn't have an FPU (by design or
       // intention), the assumptions made on the software support
       // mirror that of the equivalent hardware support *if it
       // existed*. For v7 and better we indicate that denormals are
       // flushed preserving sign, and for V6 we indicate that
       // denormals are flushed to positive zero.

test/CodeGen/ARM/build-attributes.ll

 ; This tests that MC/asm header conversion is smooth and that the
 ; build attributes are correct
 
 ; RUN: llc < %s -mtriple=thumbv5-linux-gnueabi -mcpu=xscale | FileCheck %s --check-prefix=XSCALE
 ; RUN: llc < %s -mtriple=armv6-linux-gnueabi | FileCheck %s --check-prefix=V6
 ; RUN: llc < %s -mtriple=armv6-linux-gnueabi -enable-unsafe-fp-math | FileCheck %s --check-prefix=V6-FAST
+; RUN: llc < %s -mtriple=armv6-linux-gnueabi -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=thumbv6m-linux-gnueabi | FileCheck %s --check-prefix=V6M
 ; RUN: llc < %s -mtriple=thumbv6m-linux-gnueabi -enable-unsafe-fp-math | FileCheck %s --check-prefix=V6M-FAST
 ; RUN: llc < %s -mtriple=armv6-linux-gnueabi -mcpu=arm1156t2f-s | FileCheck %s --check-prefix=ARM1156T2F-S
 ; RUN: llc < %s -mtriple=armv6-linux-gnueabi -mcpu=arm1156t2f-s -enable-unsafe-fp-math  | FileCheck %s --check-prefix=ARM1156T2F-S-FAST
+; RUN: llc < %s -mtriple=armv6-linux-gnueabi -mcpu=arm1156t2f-s -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=thumbv7m-linux-gnueabi | FileCheck %s --check-prefix=V7M
 ; RUN: llc < %s -mtriple=thumbv7m-linux-gnueabi -enable-unsafe-fp-math | FileCheck %s --check-prefix=V7M-FAST
+; RUN: llc < %s -mtriple=thumbv7m-linux-gnueabi -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi | FileCheck %s --check-prefix=V7
+; RUN: llc < %s -mtriple=armv7-linux-gnueabi -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -enable-unsafe-fp-math | FileCheck %s --check-prefix=V7-FAST
 ; RUN: llc < %s -mtriple=armv8-linux-gnueabi | FileCheck %s --check-prefix=V8
 ; RUN: llc < %s -mtriple=armv8-linux-gnueabi -enable-unsafe-fp-math | FileCheck %s --check-prefix=V8-FAST
+; RUN: llc < %s -mtriple=armv8-linux-gnueabi -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=thumbv8-linux-gnueabi | FileCheck %s --check-prefix=Vt8
+; RUN: llc < %s -mtriple=thumbv8-linux-gnueabi -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=armv8-linux-gnueabi -mattr=-neon,-crypto | FileCheck %s --check-prefix=V8-FPARMv8
 ; RUN: llc < %s -mtriple=armv8-linux-gnueabi -mattr=-fp-armv8,-crypto | FileCheck %s --check-prefix=V8-NEON
 ; RUN: llc < %s -mtriple=armv8-linux-gnueabi -mattr=-crypto | FileCheck %s --check-prefix=V8-FPARMv8-NEON
 ; RUN: llc < %s -mtriple=armv8-linux-gnueabi | FileCheck %s --check-prefix=V8-FPARMv8-NEON-CRYPTO
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a5 | FileCheck %s --check-prefix=CORTEX-A5-DEFAULT
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a5 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A5-DEFAULT-FAST
+; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a5 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a5 -mattr=-neon,+d16 | FileCheck %s --check-prefix=CORTEX-A5-NONEON
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a5 -mattr=-vfp2 | FileCheck %s --check-prefix=CORTEX-A5-NOFPU
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a5 -mattr=-vfp2 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A5-NOFPU-FAST
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a9 -float-abi=soft | FileCheck %s --check-prefix=CORTEX-A9-SOFT
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a9 -float-abi=soft -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A9-SOFT-FAST
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a9 -float-abi=hard | FileCheck %s --check-prefix=CORTEX-A9-HARD
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a9 -float-abi=hard -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A9-HARD-FAST
+; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a9 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a12 | FileCheck %s --check-prefix=CORTEX-A12-DEFAULT
+; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a9 -float-abi=soft | FileCheck %s --check-prefix=CORTEX-A9-SOFT
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a12 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A12-DEFAULT-FAST
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a12 -mattr=-vfp2 | FileCheck %s --check-prefix=CORTEX-A12-NOFPU
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a12 -mattr=-vfp2 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A12-NOFPU-FAST
+; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a12 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a15 | FileCheck %s --check-prefix=CORTEX-A15
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a15 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A15-FAST
+; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a15 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a17 | FileCheck %s --check-prefix=CORTEX-A17-DEFAULT
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a17 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A17-FAST
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a17 -mattr=-vfp2 | FileCheck %s --check-prefix=CORTEX-A17-NOFPU
 ; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a17 -mattr=-vfp2 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A17-NOFPU-FAST
+; RUN: llc < %s -mtriple=armv7-linux-gnueabi -mcpu=cortex-a17 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=thumbv6m-linux-gnueabi -mcpu=cortex-m0 | FileCheck %s --check-prefix=CORTEX-M0
 ; RUN: llc < %s -mtriple=thumbv6m-linux-gnueabi -mcpu=cortex-m0 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-M0-FAST
+; RUN: llc < %s -mtriple=thumbv6m-linux-gnueabi -mcpu=cortex-m0 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=thumbv7m-linux-gnueabi -mcpu=cortex-m3 | FileCheck %s --check-prefix=CORTEX-M3
 ; RUN: llc < %s -mtriple=thumbv7m-linux-gnueabi -mcpu=cortex-m3 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-M3-FAST
+; RUN: llc < %s -mtriple=thumbv7m-linux-gnueabi -mcpu=cortex-m3 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=thumbv7m-linux-gnueabi -mcpu=cortex-m4 -float-abi=soft | FileCheck %s --check-prefix=CORTEX-M4-SOFT
 ; RUN: llc < %s -mtriple=thumbv7m-linux-gnueabi -mcpu=cortex-m4 -float-abi=soft -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-M4-SOFT-FAST
 ; RUN: llc < %s -mtriple=thumbv7m-linux-gnueabi -mcpu=cortex-m4 -float-abi=hard | FileCheck %s --check-prefix=CORTEX-M4-HARD
 ; RUN: llc < %s -mtriple=thumbv7m-linux-gnueabi -mcpu=cortex-m4 -float-abi=hard -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-M4-HARD-FAST
+; RUN: llc < %s -mtriple=thumbv7m-linux-gnueabi -mcpu=cortex-m4 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=thumbv7em-linux-gnueabi -mcpu=cortex-m7 -mattr=-vfp2 | FileCheck %s --check-prefix=CORTEX-M7 --check-prefix=CORTEX-M7-SOFT
 ; RUN: llc < %s -mtriple=thumbv7em-linux-gnueabi -mcpu=cortex-m7 -mattr=-vfp2 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-M7-NOFPU-FAST
 ; RUN: llc < %s -mtriple=thumbv7em-linux-gnueabi -mcpu=cortex-m7 -mattr=+fp-only-sp | FileCheck %s --check-prefix=CORTEX-M7 --check-prefix=CORTEX-M7-SINGLE
 ; RUN: llc < %s -mtriple=thumbv7em-linux-gnueabi -mcpu=cortex-m7 -mattr=+fp-only-sp -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-M7-FAST
 ; RUN: llc < %s -mtriple=thumbv7em-linux-gnueabi -mcpu=cortex-m7 | FileCheck %s --check-prefix=CORTEX-M7-DOUBLE
+; RUN: llc < %s -mtriple=thumbv7em-linux-gnueabi -mcpu=cortex-m7 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=armv7r-linux-gnueabi -mcpu=cortex-r5 | FileCheck %s --check-prefix=CORTEX-R5
 ; RUN: llc < %s -mtriple=armv7r-linux-gnueabi -mcpu=cortex-r5 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-R5-FAST
+; RUN: llc < %s -mtriple=armv7r-linux-gnueabi -mcpu=cortex-r5 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=armv8-linux-gnueabi -mcpu=cortex-a53 | FileCheck %s --check-prefix=CORTEX-A53
 ; RUN: llc < %s -mtriple=armv8-linux-gnueabi -mcpu=cortex-a53 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A53-FAST
+; RUN: llc < %s -mtriple=armv8-linux-gnueabi -mcpu=cortex-a53 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=armv8-linux-gnueabi -mcpu=cortex-a57 | FileCheck %s --check-prefix=CORTEX-A57
 ; RUN: llc < %s -mtriple=armv8-linux-gnueabi -mcpu=cortex-a57 -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A57-FAST
+; RUN: llc < %s -mtriple=armv8-linux-gnueabi -mcpu=cortex-a57 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 | FileCheck %s  --check-prefix=CORTEX-A7-CHECK
 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -enable-unsafe-fp-math | FileCheck %s  --check-prefix=CORTEX-A7-CHECK-FAST
 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -mattr=-vfp2,-vfp3,-vfp4,-neon | FileCheck %s --check-prefix=CORTEX-A7-NOFPU
 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -mattr=-vfp2,-vfp3,-vfp4,-neon -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A7-NOFPU-FAST
 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -mattr=+vfp4,-neon | FileCheck %s --check-prefix=CORTEX-A7-FPUV4
 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -mattr=+vfp4,-neon -enable-unsafe-fp-math | FileCheck %s --check-prefix=CORTEX-A7-FPUV4-FAST
 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -mattr=+vfp4,,+d16,-neon | FileCheck %s --check-prefix=CORTEX-A7-FPUV4
+; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -enable-sign-dependent-rounding-fp-math | FileCheck %s --check-prefix=DYN-ROUNDING
 ; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -relocation-model=pic | FileCheck %s --check-prefix=RELOC-PIC
 ; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -relocation-model=static | FileCheck %s --check-prefix=RELOC-OTHER
 ; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -relocation-model=default | FileCheck %s --check-prefix=RELOC-OTHER
 ; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -relocation-model=dynamic-no-pic | FileCheck %s --check-prefix=RELOC-OTHER
 ; RUN: llc < %s -mtriple=arm-none-linux-gnueabi | FileCheck %s --check-prefix=RELOC-OTHER
 ; RUN: llc < %s -mtriple=arm-none-linux-gnueabi | FileCheck %s --check-prefix=PCS-R9-USE
 ; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -arm-reserve-r9 | FileCheck %s --check-prefix=PCS-R9-RESERVE
 

 ; RUN: llc < %s -mtriple=armv5-none-linux-gnueabi -mcpu=arm1022e -arm-no-strict-align | FileCheck %s --check-prefix=NO-STRICT-ALIGN
 ; RUN: llc < %s -mtriple=armv5-none-linux-gnueabi -mcpu=arm1022e -arm-strict-align | FileCheck %s --check-prefix=STRICT-ALIGN
 ; RUN: llc < %s -mtriple=armv5-none-linux-gnueabi -mcpu=arm1022e | FileCheck %s --check-prefix=STRICT-ALIGN
 
 ; XSCALE:      .eabi_attribute 6, 5
 ; XSCALE:      .eabi_attribute 8, 1
 ; XSCALE:      .eabi_attribute 9, 1
 
+; DYN-ROUNDING: .eabi_attribute 19, 1
+
 ; V6:   .eabi_attribute 6, 6
 ; V6:   .eabi_attribute 8, 1
 ;; We assume round-to-nearest by default (matches GCC)
 ; V6-NOT:   .eabi_attribute 19
 ;; The default choice made by llc is for a V6 CPU without an FPU.
 ;; This is not an interesting detail, but for such CPUs, the default intention is to use
 ;; software floating-point support. The choice is not important for targets without
 ;; FPU support!