[clang][RISCV] Fix incorrect ABI lowering for inherited structs under hard-float ABIs

The hard float ABIs have a rule that if a flattened struct contains
either a single fp value, or an int+fp, or fp+fp then it may be passed
in a pair of registers (if sufficient GPRs+FPRs are available).
detectFPCCEligibleStruct and the helper it calls,
detectFPCCEligibleStructHelper examine the type of the argument/return
value to determine if it complies with the requirements for this ABI
rule.

As reported in bug #57084, this logic produces incorrect results for C++
structs that inherit from other structs. This is because only the fields
of the struct were examined, but enumerating RD->fields misses any
fields in inherited C++ structs. This patch corrects that issue by
adding appropriate logic to enumerate any included base structs.

Differential Revision: https://reviews.llvm.org/D131677

Author: asb

clang/lib/CodeGen/TargetInfo.cpp

@@ -10979,9 +10979,22 @@ bool RISCVABIInfo::detectFPCCEligibleStructHelper(QualType Ty, CharUnits CurOff,
     // Unions aren't eligible unless they're empty (which is caught above).
     if (RD->isUnion())
       return false;
+    const ASTRecordLayout &Layout = getContext().getASTRecordLayout(RD);
+    // If this is a C++ record, check the bases first.
+    if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
+      for (const CXXBaseSpecifier &B : CXXRD->bases()) {
+        const auto *BDecl =
+            cast<CXXRecordDecl>(B.getType()->castAs<RecordType>()->getDecl());
+        CharUnits BaseOff = Layout.getBaseClassOffset(BDecl);
+        bool Ret = detectFPCCEligibleStructHelper(B.getType(), CurOff + BaseOff,
+                                                  Field1Ty, Field1Off, Field2Ty,
+                                                  Field2Off);
+        if (!Ret)
+          return false;
+      }
+    }
     int ZeroWidthBitFieldCount = 0;
     for (const FieldDecl *FD : RD->fields()) {
-      const ASTRecordLayout &Layout = getContext().getASTRecordLayout(RD);
       uint64_t FieldOffInBits = Layout.getFieldOffset(FD->getFieldIndex());
       QualType QTy = FD->getType();
       if (FD->isBitField()) {

clang/test/CodeGen/RISCV/riscv-abi.cpp

@@ -1,15 +1,15 @@
-// RUN: %clang_cc1 -triple riscv32 -emit-llvm -x c++ %s -o - \
+// RUN: %clang_cc1 -triple riscv32 -emit-llvm %s -o - \
 // RUN:   | FileCheck -check-prefixes=ILP32,ILP32-ILP32F,ILP32-ILP32F-ILP32D %s
-// RUN: %clang_cc1 -triple riscv32 -target-feature +f -target-abi ilp32f -emit-llvm -x c++ %s -o - \
+// RUN: %clang_cc1 -triple riscv32 -target-feature +f -target-abi ilp32f -emit-llvm %s -o - \
 // RUN:   | FileCheck -check-prefixes=ILP32F,ILP32-ILP32F,ILP32F-ILP32D,ILP32-ILP32F-ILP32D %s
-// RUN: %clang_cc1 -triple riscv32 -target-feature +f -target-feature +d -target-abi ilp32d -emit-llvm %s -x c++ -o - \
+// RUN: %clang_cc1 -triple riscv32 -target-feature +f -target-feature +d -target-abi ilp32d -emit-llvm %s -o - \
 // RUN:   | FileCheck -check-prefixes=ILP32D,ILP32F-ILP32D,ILP32-ILP32F-ILP32D %s
 
-// RUN: %clang_cc1 -triple riscv64 -emit-llvm -x c++ %s -o - \
+// RUN: %clang_cc1 -triple riscv64 -emit-llvm %s -o - \
 // RUN:   | FileCheck -check-prefixes=LP64,LP64-LP64F,LP64-LP64F-LP64D %s
-// RUN: %clang_cc1 -triple riscv64 -target-feature +f -target-abi lp64f -emit-llvm -x c++ %s -o - \
+// RUN: %clang_cc1 -triple riscv64 -target-feature +f -target-abi lp64f -emit-llvm %s -o - \
 // RUN:   | FileCheck -check-prefixes=LP64F,LP64-LP64F,LP64F-LP64D,LP64-LP64F-LP64D %s
-// RUN: %clang_cc1 -triple riscv64 -target-feature +f -target-feature +d -target-abi lp64d -emit-llvm %s -x c++ -o - \
+// RUN: %clang_cc1 -triple riscv64 -target-feature +f -target-feature +d -target-abi lp64d -emit-llvm %s -o - \
 // RUN:   | FileCheck -check-prefixes=LP64D,LP64F-LP64D,LP64-LP64F-LP64D %s
 
 #include <stdint.h>
@@ -39,12 +39,10 @@ struct child2_float_s : parent2_int32_s {
   float f1;
 };
 
-// TODO: Fix incorrect lowering for hard-float ABIs.
-
 // ILP32: define{{.*}} [2 x i32] @_Z30int32_float_struct_inheritance14child2_float_s([2 x i32] %a.coerce)
-// ILP32F-ILP32D: define{{.*}} float @_Z30int32_float_struct_inheritance14child2_float_s(float %0)
+// ILP32F-ILP32D: define{{.*}} { i32, float } @_Z30int32_float_struct_inheritance14child2_float_s(i32 %0, float %1)
 // LP64: define{{.*}} i64 @_Z30int32_float_struct_inheritance14child2_float_s(i64 %a.coerce)
-// LP64F-LP64D: define{{.*}} float @_Z30int32_float_struct_inheritance14child2_float_s(float %0)
+// LP64F-LP64D: define{{.*}} { i32, float } @_Z30int32_float_struct_inheritance14child2_float_s(i32 %0, float %1)
 struct child2_float_s int32_float_struct_inheritance(struct child2_float_s a) {
   return a;
 }
@@ -57,10 +55,9 @@ struct child3_int64_s : parent3_float_s {
   int64_t i1;
 };
 
-// TODO: Fix incorrect lowering for lp64f/lp64d ABIs.
-
 // ILP32-ILP32F-ILP32D-LABEL: define{{.*}} void @_Z30float_int64_struct_inheritance14child3_int64_s(ptr noalias sret(%struct.child3_int64_s)
-// LP64-LP64F-LP64D-LABEL: define{{.*}} [2 x i64] @_Z30float_int64_struct_inheritance14child3_int64_s([2 x i64] %a.coerce)
+// LP64-LABEL: define{{.*}} [2 x i64] @_Z30float_int64_struct_inheritance14child3_int64_s([2 x i64] %a.coerce)
+// LP64F-LP64D-LABEL: define{{.*}} { float, i64 } @_Z30float_int64_struct_inheritance14child3_int64_s(float %0, i64 %1)
 struct child3_int64_s float_int64_struct_inheritance(struct child3_int64_s a) {
   return a;
 }
@@ -73,16 +70,54 @@ struct child4_double_s : parent4_double_s {
   double d1;
 };
 
-// TODO: Fix incorrect lowering for ilp32d/lp64d ABIs.
-
 // ILP32-ILP32F-LABEL: define{{.*}} void @_Z32double_double_struct_inheritance15child4_double_s(ptr noalias sret(%struct.child4_double_s)
-// ILP32D-LABEL: define{{.*}} double @_Z32double_double_struct_inheritance15child4_double_s(double %0)
+// ILP32D-LABEL: define{{.*}} { double, double } @_Z32double_double_struct_inheritance15child4_double_s(double %0, double %1)
 // LP64-LP64F-LABEL: define{{.*}} [2 x i64] @_Z32double_double_struct_inheritance15child4_double_s([2 x i64] %a.coerce)
-// LP64D-LABEL: define{{.*}} double @_Z32double_double_struct_inheritance15child4_double_s(double %0)
+// LP64D-LABEL: define{{.*}} { double, double } @_Z32double_double_struct_inheritance15child4_double_s(double %0, double %1)
 struct child4_double_s double_double_struct_inheritance(struct child4_double_s a) {
   return a;
 }
 
+// When virtual inheritance is used, the resulting struct isn't eligible for
+// passing in registers.
+
+struct parent5_virtual_s {
+  int32_t i1;
+};
+
+struct child5_virtual_s : virtual parent5_virtual_s {
+  float f1;
+};
+
+// ILP32-ILP32F-ILP32D-LABEL: define{{.*}} void @_ZN16child5_virtual_sC1EOS_(ptr noundef nonnull align 4 dereferenceable(8) %this, ptr noundef nonnull align 4 dereferenceable(8) %0)
+// LP64-LP64F-LP64D-LABEL: define{{.*}} void @_ZN16child5_virtual_sC1EOS_(ptr noundef nonnull align 8 dereferenceable(12) %this, ptr noundef nonnull align 8 dereferenceable(12) %0)
+struct child5_virtual_s int32_float_virtual_struct_inheritance(struct child5_virtual_s a) {
+  return a;
+}
+
+// Check for correct lowering in the presence of diamond inheritance.
+
+struct parent6_float_s {
+  float f1;
+};
+
+struct child6a_s : parent6_float_s {
+};
+
+struct child6b_s : parent6_float_s {
+};
+
+struct grandchild_6_s : child6a_s, child6b_s {
+};
+
+// ILP32: define{{.*}} [2 x i32] @_Z38float_float_diamond_struct_inheritance14grandchild_6_s([2 x i32] %a.coerce)
+// ILP32F-ILP64D: define{{.*}} { float, float } @_Z38float_float_diamond_struct_inheritance14grandchild_6_s(float %0, float %1)
+// LP64: define{{.*}} i64 @_Z38float_float_diamond_struct_inheritance14grandchild_6_s(i64 %a.coerce)
+// LP64F-LP64D: define{{.*}} { float, float } @_Z38float_float_diamond_struct_inheritance14grandchild_6_s(float %0, float %1)
+struct grandchild_6_s float_float_diamond_struct_inheritance(struct grandchild_6_s a) {
+  return a;
+}
+
 // NOTE: These prefixes are unused. Do not add tests below this line:
 // ILP32F: {{.*}}
 // LP64F: {{.*}}