This patch fixes DWARF frame calculations for functions that use alloca
on AMD GCN.
Like many other platforms, it achieves this by switching to
frame-pointer mode for this function.
The frame pointer is necessary for debugability only, so if the user
specifies -fomit-frame-pointer then this is honoured.
Committed to devel/omp/gcc-10. The prerequisite CFI patches don't exist
on mainline yet.
Andrew
amdgcn: Fix DWARF variables with alloca
Require a frame pointer for entry functions that use alloca because it isn't
possible to encode the DWARF frame otherwise. Adjust the CFA definition
expressions accordingly.
gcc/ChangeLog:
* config/gcn/gcn.c (gcn_expand_prologue): Use the frame pointer for
the DWARF CFA, if it exists.
(gcn_frame_pointer_rqd): Require a frame pointer for entry functions
that use alloca.
diff --git a/gcc/config/gcn/gcn.c b/gcc/config/gcn/gcn.c
index ea88b5e9124..1cb92714f24 100644
--- a/gcc/config/gcn/gcn.c
+++ b/gcc/config/gcn/gcn.c
@@ -3009,6 +3009,16 @@ gcn_expand_prologue ()
gen_rtx_SET (sp, gen_rtx_PLUS (DImode, sp,
dbg_adjustment)));
+ if (offsets->need_frame_pointer)
+ {
+ /* Set the CFA to the entry stack address, as an offset from the
+ frame pointer. This is necessary when alloca is used, and
+ harmless otherwise. */
+ rtx neg_adjust = gen_int_mode (-offsets->callee_saves, DImode);
+ add_reg_note (insn, REG_CFA_DEF_CFA,
+ gen_rtx_PLUS (DImode, fp, neg_adjust));
+ }
+
/* Make sure the flat scratch reg doesn't get optimised away. */
emit_insn (gen_prologue_use (gen_rtx_REG (DImode, FLAT_SCRATCH_REG)));
}
@@ -3120,10 +3130,13 @@ bool
gcn_frame_pointer_rqd (void)
{
/* GDB needs the frame pointer in order to unwind properly,
- but that's not important for the entry point.
- We should also repect the -fomit-frame-pointer flag. */
- return (cfun && cfun->machine && cfun->machine->normal_function
- && !flag_omit_frame_pointer);
+ but that's not important for the entry point, unless alloca is used.
+ It's not important for code execution, so we should repect the
+ -fomit-frame-pointer flag. */
+ return (!flag_omit_frame_pointer
+ && cfun
+ && (cfun->calls_alloca
+ || (cfun->machine && cfun->machine->normal_function)));
}
/* Implement TARGET_CAN_ELIMINATE.
