[mips] Mark aggregates returned in registers with the 'inreg' attribute.

[dsanders]

Summary

This allows us to easily find them in the backend after the aggregates have
been lowered to other types. This is important on big-endian targets using
the N32/N64 ABI's since these ABI's must shift small structures into the
upper bits of the register.

[atanasyan]

LGTM

lib/CodeGen/TargetInfo.cpp

5535

Does it have a sense to join two if conditions below into the single one?

if (!IsO32 || (RetTy->isVectorType() && !RetTy->hasFloatingRepresentation())) {
  ABIArgInfo ArgInfo = ABIArgInfo::getDirect(returnAggregateInRegs(RetTy, Size));
  ArgInfo.setInReg(true);
  return ArgInfo;
}

[dsanders]

Thanks

lib/CodeGen/TargetInfo.cpp

5535

Yes, with an extra comment mentioning the N32/N64. It looked a bit misleading merging the if-statements while only mentioning the O32 case in the comment.

I'll make this change before committing.

lib/CodeGen/TargetInfo.cpp

ABIArgInfo MipsABIInfo::classifyReturnType(QualType RetTy) const {
   if (!IsO32 && Size == 0)
     return ABIArgInfo::getIgnore();
 
   if (isAggregateTypeForABI(RetTy) || RetTy->isVectorType()) {
     if (Size <= 128) {
       if (RetTy->isAnyComplexType())
         return ABIArgInfo::getDirect();
 
       // O32 returns integer vectors in registers.
-      if (IsO32 && RetTy->isVectorType() && !RetTy->hasFloatingRepresentation())
-        return ABIArgInfo::getDirect(returnAggregateInRegs(RetTy, Size));
+      if (IsO32 && RetTy->isVectorType() &&
+          !RetTy->hasFloatingRepresentation()) {
+        ABIArgInfo ArgInfo =
+            ABIArgInfo::getDirect(returnAggregateInRegs(RetTy, Size));
+        ArgInfo.setInReg(true);
+        return ArgInfo;
+      }
 
-      if (!IsO32)
-        return ABIArgInfo::getDirect(returnAggregateInRegs(RetTy, Size));
+      if (!IsO32) {
+        ABIArgInfo ArgInfo =
+            ABIArgInfo::getDirect(returnAggregateInRegs(RetTy, Size));
+        ArgInfo.setInReg(true);
+        return ArgInfo;
+      }
     }
 
     return ABIArgInfo::getIndirect(0);
   }
 
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
     RetTy = EnumTy->getDecl()->getIntegerType();

test/CodeGen/mips-vector-return.c

 // RUN: %clang -target mipsel-unknown-linux -O3 -S -o - -emit-llvm %s | FileCheck %s -check-prefix=O32
 // RUN: %clang -target mips64el-unknown-linux -O3 -S -mabi=n64 -o - -emit-llvm %s | FileCheck %s -check-prefix=N64
 
 // vectors larger than 16-bytes are returned via the hidden pointer argument. 
 // N64/N32 returns vectors whose size is equal to or smaller than 16-bytes in
 // integer registers. 
 typedef float  v4sf __attribute__ ((__vector_size__ (16)));
 typedef double v4df __attribute__ ((__vector_size__ (32)));
 typedef int v4i32 __attribute__ ((__vector_size__ (16)));
 
 // O32-LABEL: define void @test_v4sf(<4 x float>* noalias nocapture sret
-// N64: define { i64, i64 } @test_v4sf
+// N64: define inreg { i64, i64 } @test_v4sf
 v4sf test_v4sf(float a) {
   return (v4sf){0.0f, a, 0.0f, 0.0f};
 }
 
 // O32-LABEL: define void @test_v4df(<4 x double>* noalias nocapture sret
 // N64-LABEL: define void @test_v4df(<4 x double>* noalias nocapture sret
 v4df test_v4df(double a) {
   return (v4df){0.0, a, 0.0, 0.0};
 }
 
 // O32 returns integer vectors whose size is equal to or smaller than 16-bytes
 // in integer registers.
 //
-// O32: define { i32, i32, i32, i32 } @test_v4i32
-// N64: define { i64, i64 } @test_v4i32
+// O32: define inreg { i32, i32, i32, i32 } @test_v4i32
+// N64: define inreg { i64, i64 } @test_v4i32
 v4i32 test_v4i32(int a) {
   return (v4i32){0, a, 0, 0};
 }
 

test/CodeGen/mips64-class-return.cpp

 class D2 : public B0 {
   double d2;
 };
 
 extern D0 gd0;
 extern D1 gd1;
 extern D2 gd2;
 
-// CHECK: define { i64, i64 } @_Z4foo1v() 
+// CHECK: define inreg { i64, i64 } @_Z4foo1v()
 D0 foo1(void) {
   return gd0;
 }
 
-// CHECK: define { double, float } @_Z4foo2v() 
+// CHECK: define inreg { double, float } @_Z4foo2v()
 D1 foo2(void) {
   return gd1;
 }
 
-// CHECK-LABEL: define void @_Z4foo32D2(i64 %a0.coerce0, double %a0.coerce1) 
+// CHECK-LABEL: define void @_Z4foo32D2(i64 %a0.coerce0, double %a0.coerce1)
 void foo3(D2 a0) {
   gd2 = a0;
 }
 
 // CHECK-LABEL: define void @_Z4foo42D0(i64 %a0.coerce0, i64 %a0.coerce1)
 void foo4(D0 a0) {
   gd0 = a0;
 }