https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77359
--- Comment #8 from Dominik Vogt <vogt at linux dot vnet.ibm.com> ---
Something like this:
-- snip --
diff --git a/gcc/config/rs6000/rs6000.h b/gcc/config/rs6000/rs6000.h
index 353f388..3158c24 100644
--- a/gcc/config/rs6000/rs6000.h
+++ b/gcc/config/rs6000/rs6000.h
@@ -1719,6 +1719,11 @@ extern enum reg_class
rs6000_constraints[RS6000_CONSTRAINT_MAX];
(TARGET_ALTIVEC || TARGET_VSX) ? 16 : 8) \
+ RS6000_SAVE_AREA))
+/* Rounds up BYTE_SIZE (in bytes) to the guaranteed alignment of the dynamic
+ stack offset. */
+#define STACK_DYNAMIC_OFFSET_ALIGN(byte_size) \
+ (RS6000_ALIGN (byte_size, (TARGET_ALTIVEC || TARGET_VSX) ? 16 : 8))
+
/* Offset from the stack pointer register to an item dynamically
allocated on the stack, e.g., by `alloca'.
@@ -1726,9 +1731,8 @@ extern enum reg_class
rs6000_constraints[RS6000_CONSTRAINT_MAX];
length of the outgoing arguments. The default is correct for most
machines. See `function.c' for details. */
#define STACK_DYNAMIC_OFFSET(FUNDECL) \
- (RS6000_ALIGN (crtl->outgoing_args_size, \
- (TARGET_ALTIVEC || TARGET_VSX) ? 16 : 8) \
- + (STACK_POINTER_OFFSET))
+ (STACK_DYNAMIC_OFFSET_ALIGN(crtl->outgoing_args_size)
\
+ (STACK_POINTER_OFFSET))
/* If we generate an insn to push BYTES bytes,
this says how many the stack pointer really advances by.
diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index 99f052d..5ec68ae 100644
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -5717,6 +5717,13 @@ init_emit (void)
REGNO_POINTER_ALIGN (VIRTUAL_CFA_REGNUM) = BITS_PER_WORD;
#endif
+#ifdef STACK_DYNAMIC_OFFSET_ALIGN
+ REGNO_POINTER_ALIGN (VIRTUAL_STACK_DYNAMIC_REGNUM) =
+ STACK_DYNAMIC_OFFSET_ALIGN (1);
+ gcc_assert (REGNO_POINTER_ALIGN (VIRTUAL_STACK_DYNAMIC_REGNUM)
+ <= REGNO_POINTER_ALIGN (STACK_POINTER_REGNUM));
+#endif
+
#ifdef INIT_EXPANDERS
INIT_EXPANDERS;
#endif
-- snip --
