[mips] Correct ELF e_flags for the N32 ABI when using a mips-* triple rather than a mips64-* triple

[dsanders]

Summary

Generally speaking, mips-* vs mips64-* should not be used to make decisions
about the content or format of the ELF. This should be based on the ABI
and CPU in use. For example, mips-linux-gnu-clang -mips64r2 -mabi=64
should produce an ELF64 as should mips64-linux-gnu-clang -mabi=64.
Conversely, mips64-linux-gnu-clang -mabi=n32 should produce an ELF32 as
should mips-linux-gnu-clang -mips64r2 -mabi=n32.

This patch fixes the e_flags but leaves the ELF32 vs ELF64 issue for now
since there is no apparent way to base this decision on the ABI and CPU.

[sstankovic]

LGTM

lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp

else if (Features & Mips::FeatureMips32r2)
     EFlags |= ELF::EF_MIPS_ARCH_32R2;
   else if (Features & Mips::FeatureMips32)
     EFlags |= ELF::EF_MIPS_ARCH_32;
   else if (Features & Mips::FeatureMips2)
     EFlags |= ELF::EF_MIPS_ARCH_2;
   else
     EFlags |= ELF::EF_MIPS_ARCH_1;
 
-  if (T.isArch64Bit()) {
-    if (Features & Mips::FeatureN32)
-      EFlags |= ELF::EF_MIPS_ABI2;
-    else if (Features & Mips::FeatureO32) {
-      EFlags |= ELF::EF_MIPS_ABI_O32;
+  // ABI
+  // N64 does not require any ABI bits.
+  if (Features & Mips::FeatureO32)
+  else if (Features & Mips::FeatureN32)
+    EFlags |= ELF::EF_MIPS_ABI2;
+
+  if (Features & Mips::FeatureGP64Bit) {
+    if (Features & Mips::FeatureO32)
       EFlags |= ELF::EF_MIPS_32BITMODE; /* Compatibility Mode */
-    }
-    // No need to set any bit for N64 which is the default ABI at the moment
-    // for 64-bit Mips architectures.
-  } else {
-    if (Features & Mips::FeatureMips64r2 || Features & Mips::FeatureMips64)
-      EFlags |= ELF::EF_MIPS_32BITMODE;
+  } else if (Features & Mips::FeatureMips64r2 || Features & Mips::FeatureMips64)
 
-    // ABI
-    EFlags |= ELF::EF_MIPS_ABI_O32;
-  }
-
   // Other options.
   if (Features & Mips::FeatureNaN2008)
     EFlags |= ELF::EF_MIPS_NAN2008;
 
   // -mabicalls and -mplt are not implemented but we should act as if they were
   // given.
   EFlags |= ELF::EF_MIPS_CPIC;
   if (Features & Mips::FeatureN64)

test/MC/Mips/elf_eflags.s

 # These *MUST* match the output of 'gcc -c' compiled with the same triple and
 # corresponding options (-mcpu=mips32 -> -mips32 for example).
 
 # RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips64r6 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPSEL-MIPS64R6 %s
-# MIPSEL-MIPS64R6: Flags [ (0xA0001506)
+# MIPSEL-MIPS64R6: Flags [ (0xA0000406)
 
 # RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips64r6 -mattr=+nan2008 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPSEL-MIPS64R6-NAN2008 %s
-# MIPSEL-MIPS64R6-NAN2008: Flags [ (0xA0001506)
+# MIPSEL-MIPS64R6-NAN2008: Flags [ (0xA0000406)
 
 # RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips64r2 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPSEL-MIPS64R2 %s
-# MIPSEL-MIPS64R2: Flags [ (0x80001106)
+# MIPSEL-MIPS64R2: Flags [ (0x80000006)
 
 # RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips64r2 -mattr=+nan2008 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPSEL-MIPS64R2-NAN2008 %s
-# MIPSEL-MIPS64R2-NAN2008: Flags [ (0x80001506)
+# MIPSEL-MIPS64R2-NAN2008: Flags [ (0x80000406)
 
 # RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips64 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPSEL-MIPS64 %s
-# MIPSEL-MIPS64: Flags [ (0x60001106)
+# MIPSEL-MIPS64: Flags [ (0x60000006)
 
 # RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips64 -mattr=+nan2008 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPSEL-MIPS64-NAN2008 %s
-# MIPSEL-MIPS64-NAN2008: Flags [ (0x60001506)
+# MIPSEL-MIPS64-NAN2008: Flags [ (0x60000406)
 
 # RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips32r6 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPSEL-MIPS32R6 %s
 # MIPSEL-MIPS32R6: Flags [ (0x90001404)
 
 # RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips32r6 -mattr=+nan2008 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPSEL-MIPS32R6-NAN2008 %s
 # MIPSEL-MIPS32R6-NAN2008: Flags [ (0x90001404)
 
 # RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips32r2 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPSEL-MIPS32R2 %s
 # MIPSEL-MIPS32R2: Flags [ (0x70001004)
 
 # RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips32r2 -mattr=+nan2008 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPSEL-MIPS32R2-NAN2008 %s
 # MIPSEL-MIPS32R2-NAN2008: Flags [ (0x70001404)
 
 # RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips32 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPSEL-MIPS32 %s
 # MIPSEL-MIPS32: Flags [ (0x50001004)
 
 # RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips32 -mattr=+nan2008 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPSEL-MIPS32-NAN2008 %s
 # MIPSEL-MIPS32-NAN2008: Flags [ (0x50001404)
 
+# RUN: llvm-mc -filetype=obj -triple mipsel-unknown-linux -mcpu=mips64r2 -mattr=-n64,n32 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPS64EL-MIPS64R2-N32 %s
 # RUN: llvm-mc -filetype=obj -triple mips64el-unknown-linux -mcpu=mips64r2 -mattr=-n64,n32 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPS64EL-MIPS64R2-N32 %s
 # MIPS64EL-MIPS64R2-N32: Flags [ (0x80000024)
 
 # RUN: llvm-mc -filetype=obj -triple mips64el-unknown-linux -mcpu=mips64r2 -mattr=-n64,n32,+nan2008 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPS64EL-MIPS64R2-N32-NAN2008 %s
 # MIPS64EL-MIPS64R2-N32-NAN2008: Flags [ (0x80000424)
 
 # RUN: llvm-mc -filetype=obj -triple mips64el-unknown-linux -mcpu=mips64 -mattr=-n64,n32 %s -o -| llvm-readobj -h | FileCheck --check-prefix=MIPS64EL-MIPS64-N32 %s
 # MIPS64EL-MIPS64-N32: Flags [ (0x60000024)