Documenting the status quo. This specific behavior relates to a 1994 change
(Subversion r7229, Git commit 15fc002672d643fd9d93d220027b5cd2aefc632c).
That one, however, isn't to blame here: we'd otherwise of course run into
nvptx' 'sorry, unimplemented: target cannot support alloca'.
PR target/65181
gcc/testsuite/
* gcc.target/nvptx/__builtin_alloca_0-1-O0.c: New.
* gcc.target/nvptx/__builtin_alloca_0-1-O1.c: Likewise.
---
.../nvptx/__builtin_alloca_0-1-O0.c | 37 +++++++++++++++++++
.../nvptx/__builtin_alloca_0-1-O1.c | 33 +++++++++++++++++
2 files changed, 70 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/nvptx/__builtin_alloca_0-1-O0.c
create mode 100644 gcc/testsuite/gcc.target/nvptx/__builtin_alloca_0-1-O1.c
diff --git a/gcc/testsuite/gcc.target/nvptx/__builtin_alloca_0-1-O0.c
b/gcc/testsuite/gcc.target/nvptx/__builtin_alloca_0-1-O0.c
new file mode 100644
index 000000000000..8c00a66c7387
--- /dev/null
+++ b/gcc/testsuite/gcc.target/nvptx/__builtin_alloca_0-1-O0.c
@@ -0,0 +1,37 @@
+/* Document what we run into for '__builtin_alloca(0)'. */
+
+/* { dg-do compile }
+ TODO We can't 'assemble' this -- it's invalid PTX code. */
+/* { dg-options {-O0 -mno-soft-stack} } */
+/* { dg-additional-options -save-temps } */
+/* { dg-final { check-function-bodies {** } {} } } */
+
+void sink(void *);
+
+void f(void)
+{
+ sink(__builtin_alloca(0));
+}
+/*
+** f:
+** .visible .func f
+** {
+** \.reg\.u64 (%r[0-9]+);
+** \.reg\.u64 (%r[0-9]+);
+** mov\.u64 \1, %stack;
+** mov\.u64 \2, \1;
+** {
+** \.param\.u64 %out_arg1;
+** st\.param\.u64 \[%out_arg1\], \2;
+** call sink, \(%out_arg1\);
+** }
+** ret;
+*/
+
+/* '%stack' is 'VIRTUAL_STACK_DYNAMIC_REGNUM', 'virtual_stack_dynamic_rtx'.
+ For '__builtin_alloca (0)', we get to
+ 'gcc/explow.cc:allocate_dynamic_stack_space', where 'addr' gets set to
+ 'virtual_stack_dynamic_rtx', 'size == const0_rtx', therefore 'return addr;',
+ which gets us '%stack' -- undefined (TODO).
+
+ { dg-final { scan-assembler-not {%stack} { xfail *-*-* } } } */
diff --git a/gcc/testsuite/gcc.target/nvptx/__builtin_alloca_0-1-O1.c
b/gcc/testsuite/gcc.target/nvptx/__builtin_alloca_0-1-O1.c
new file mode 100644
index 000000000000..2d61065d44d6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/nvptx/__builtin_alloca_0-1-O1.c
@@ -0,0 +1,33 @@
+/* Document what we run into for '__builtin_alloca(0)'. */
+
+/* { dg-do compile }
+ TODO We can't 'assemble' this -- it's invalid PTX code. */
+/* { dg-options {-O1 -mno-soft-stack} } */
+/* { dg-additional-options -save-temps } */
+/* { dg-final { check-function-bodies {** } {} } } */
+
+void sink(void *);
+
+void f(void)
+{
+ sink(__builtin_alloca(0));
+}
+/*
+** f:
+** .visible .func f
+** {
+** {
+** \.param\.u64 %out_arg1;
+** st\.param\.u64 \[%out_arg1\], %stack;
+** call sink, \(%out_arg1\);
+** }
+** ret;
+*/
+
+/* '%stack' is 'VIRTUAL_STACK_DYNAMIC_REGNUM', 'virtual_stack_dynamic_rtx'.
+ For '__builtin_alloca (0)', we get to
+ 'gcc/explow.cc:allocate_dynamic_stack_space', where 'addr' gets set to
+ 'virtual_stack_dynamic_rtx', 'size == const0_rtx', therefore 'return addr;',
+ which gets us '%stack' -- undefined (TODO).
+
+ { dg-final { scan-assembler-not {%stack} { xfail *-*-* } } } */
--
2.34.1
