Fix codegen for transparent_union function params

Update codegen for func param with transparent_union attr to be that of
the first union member.

This closes #76773.

Author: lei137

clang/test/CodeGen/transparent-union-type.c

@@ -0,0 +1,81 @@
+// RUN: %clang_cc1 -triple powerpc64le-linux -O2 -target-cpu pwr7 -emit-llvm \
+// RUN:   -fshort-enums %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-64
+// RUN: %clang_cc1 -triple powerpc64-linux -O2 -target-cpu pwr7 -emit-llvm \
+// RUN:   -fshort-enums %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-64
+// RUN: %clang_cc1 -triple powerpc-linux -O2 -target-cpu pwr7 -emit-llvm \
+// RUN:   -fshort-enums %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-32
+// RUN: %clang_cc1 -triple powerpc64-aix -O2 -target-cpu pwr7 -emit-llvm \
+// RUN:   -fshort-enums %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-64
+// RUN: %clang_cc1 -triple powerpc-aix -O2 -target-cpu pwr7 -emit-llvm \
+// RUN:   -fshort-enums %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-32
+// RUN: %clang_cc1 -triple riscv64-linux -O2 -emit-llvm -fshort-enums \
+// RUN:   %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-64
+// RUN: %clang_cc1 -triple riscv32-linux -O2 -emit-llvm -fshort-enums \
+// RUN:   %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-32
+// RUN: %clang_cc1 -triple i386-linux -O2 -emit-llvm -fshort-enums \
+// RUN:   %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-32
+// RUN: %clang_cc1 -triple x86_64-linux -O2 -emit-llvm -fshort-enums \
+// RUN:   %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-64
+// RUN: %clang_cc1 -triple armv7-linux -O2 -emit-llvm -fshort-enums \
+// RUN:   %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-32
+// RUN: %clang_cc1 -triple arm64 -target-abi darwinpcs -O2 -emit-llvm \
+// RUN:   -fshort-enums %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-64
+// RUN: %clang_cc1 -triple aarch64 -target-abi darwinpcs -O2 -emit-llvm \
+// RUN:   -fshort-enums %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-64
+
+typedef union tu_c {
+  signed char a;
+  signed char b;
+} tu_c_t __attribute__((transparent_union));
+
+typedef union tu_s {
+  short a;
+} tu_s_t __attribute__((transparent_union));
+
+typedef union tu_us {
+  unsigned short a;
+} tu_us_t __attribute__((transparent_union));
+
+typedef union tu_l {
+  long a;
+} tu_l_t __attribute__((transparent_union));
+
+// CHECK-LABEL: define{{.*}} void @ftest0(
+// CHECK-SAME: i8 noundef signext [[UC_COERCE:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    ret void
+void ftest0(tu_c_t uc) { }
+
+// CHECK-LABEL: define{{.*}} void @ftest1(
+// CHECK-SAME: i16 noundef signext [[UC_COERCE:%.*]]) local_unnamed_addr #[[ATTR0]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    ret void
+void ftest1(tu_s_t uc) { }
+
+// CHECK-LABEL: define{{.*}} void @ftest2(
+// CHECK-SAME: i16 noundef zeroext [[UC_COERCE:%.*]]) local_unnamed_addr #[[ATTR0]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    ret void
+void ftest2(tu_us_t uc) { }
+
+// CHECK-64-LABEL: define{{.*}} void @ftest3(
+// CHECK-64-SAME: i64 [[UC_COERCE:%.*]]) local_unnamed_addr #[[ATTR0]] {
+// CHECK-64-NEXT:  [[ENTRY:.*:]]
+// CHECK-64-NEXT:    ret void
+//
+// CHECK-32-LABEL: define{{.*}} void @ftest3(
+// CHECK-32-SAME: i32 [[UC_COERCE:%.*]]) local_unnamed_addr #[[ATTR0]] {
+// CHECK-32-NEXT:  [[ENTRY:.*:]]
+// CHECK-32-NEXT:    ret void
+void ftest3(tu_l_t uc) { }
+
+typedef union etest {
+  enum flag {red, yellow, blue} fl;
+  enum weekend {sun, sat} b;
+} etest_t __attribute__((transparent_union));
+
+// CHECK-LABEL: define{{.*}} void @ftest4(
+// CHECK-SAME: i8 noundef zeroext [[A_COERCE:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    ret void
+void ftest4(etest_t a) {}