[ARM] Honour ABI for rem under -O0 for EABI, GNUEABI, Android and Musl

At higher optimization levels, we generate the libcall for DIVREM_Ix, which is
fine: aeabi_{u|i}divmod. At -O0 we generate the one for REM_Ix, which is the
default {u}mod{q|h|s|d}i3.

This commit makes sure that we don't generate REM_Ix calls for ABIs that
don't support them (i.e. where we need to use DIVREM_Ix instead). This is
achieved by bailing out of FastISel, which can't handle non-double multi-reg
returns, and letting the legalization infrastructure expand the REM_Ix calls.

It also updates the divmod-eabi.ll test to run under -O0 as well, and adds some
Windows checks to it to make sure we don't break things for it.

Fixes PR27068

Differential Revision: https://reviews.llvm.org/D21926

llvm-svn: 275773

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/ARMFastISel.cpp b/llvm/lib/Target/ARM/ARMFastISel.cpp
index 0f11ac9a3a0..13724da5d4f 100644
--- a/llvm/lib/Target/ARM/ARMFastISel.cpp
+++ b/llvm/lib/Target/ARM/ARMFastISel.cpp
@@ -1718,6 +1718,13 @@ bool ARMFastISel::SelectRem(const Instruction *I, bool isSigned) {
   if (!isTypeLegal(Ty, VT))
     return false;
 
+  // Many ABIs do not provide a libcall for standalone remainder, so we need to
+  // use divrem (see the RTABI 4.3.1). Since FastISel can't handle non-double
+  // multi-reg returns, we'll have to bail out.
+  if (!TLI.hasStandaloneRem(VT)) {
+    return false;
+  }
+
   RTLIB::Libcall LC = RTLIB::UNKNOWN_LIBCALL;
   if (VT == MVT::i8)
     LC = isSigned ? RTLIB::SREM_I8 : RTLIB::UREM_I8;