From e6eacdc9451bbee54c80d6b85d22ba390fd2c7c4 Mon Sep 17 00:00:00 2001 From: Richard Sandiford Date: Thu, 1 Mar 2018 08:22:06 +0000 Subject: [PATCH] Tighten use of HARD_FRAME_POINTER_REGNUM in alias.c (PR 84538) RTL code needs to be consistent about whether it uses the stack pointer, the frame pointer or the argument pointer to access a given part of the frame. alias.c used this to divide accesses into three independent areas. The problem in the PR is that we did this for HARD_FRAME_POINTER_REGNUM even when the register wasn't being used as a frame pointer. We can't do that because the frame pointer is then just any old allocatable register and could certainly point to info accessed through the argument pointer or stack pointer. 2018-03-01 Richard Sandiford gcc/ PR rtl-optimization/84538 * alias.c (init_alias_target): Add commentary. (init_alias_analysis): Only give HARD_FRAME_POINTER_REGNUM a unique base value if the frame pointer is not eliminated to the stack pointer. gcc/testsuite/ PR rtl-optimization/84538 * gcc.dg/torture/pr84538.c: New test. From-SVN: r258094 --- gcc/ChangeLog | 8 ++++++++ gcc/alias.c | 18 +++++++++++++++++- gcc/testsuite/ChangeLog | 5 +++++ gcc/testsuite/gcc.dg/torture/pr84538.c | 16 ++++++++++++++++ 4 files changed, 46 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/gcc.dg/torture/pr84538.c diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 0a07f4b0a92..0d93e26a920 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,11 @@ +2018-03-01 Richard Sandiford + + PR rtl-optimization/84538 + * alias.c (init_alias_target): Add commentary. + (init_alias_analysis): Only give HARD_FRAME_POINTER_REGNUM + a unique base value if the frame pointer is not eliminated + to the stack pointer. + 2018-03-01 Tom de Vries PR rtl-optimization/83327 diff --git a/gcc/alias.c b/gcc/alias.c index 4c7965de807..5fa15cbd102 100644 --- a/gcc/alias.c +++ b/gcc/alias.c @@ -3191,12 +3191,21 @@ init_alias_target (void) && targetm.hard_regno_mode_ok (i, Pmode)) static_reg_base_value[i] = arg_base_value; + /* RTL code is required to be consistent about whether it uses the + stack pointer, the frame pointer or the argument pointer to + access a given area of the frame. We can therefore use the + base address to distinguish between the different areas. */ static_reg_base_value[STACK_POINTER_REGNUM] = unique_base_value (UNIQUE_BASE_VALUE_SP); static_reg_base_value[ARG_POINTER_REGNUM] = unique_base_value (UNIQUE_BASE_VALUE_ARGP); static_reg_base_value[FRAME_POINTER_REGNUM] = unique_base_value (UNIQUE_BASE_VALUE_FP); + + /* The above rules extend post-reload, with eliminations applying + consistently to each of the three pointers. Cope with cases in + which the frame pointer is eliminated to the hard frame pointer + rather than the stack pointer. */ if (!HARD_FRAME_POINTER_IS_FRAME_POINTER) static_reg_base_value[HARD_FRAME_POINTER_REGNUM] = unique_base_value (UNIQUE_BASE_VALUE_HFP); @@ -3329,7 +3338,14 @@ init_alias_analysis (void) /* Initialize the alias information for this pass. */ for (i = 0; i < FIRST_PSEUDO_REGISTER; i++) - if (static_reg_base_value[i]) + if (static_reg_base_value[i] + /* Don't treat the hard frame pointer as special if we + eliminated the frame pointer to the stack pointer instead. */ + && !(i == HARD_FRAME_POINTER_REGNUM + && reload_completed + && !frame_pointer_needed + && targetm.can_eliminate (FRAME_POINTER_REGNUM, + STACK_POINTER_REGNUM))) { new_reg_base_value[i] = static_reg_base_value[i]; bitmap_set_bit (reg_seen, i); diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index aac49641416..6528ac0276d 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2018-03-01 Richard Sandiford + + PR rtl-optimization/84538 + * gcc.dg/torture/pr84538.c: New test. + 2018-02-28 Martin Sebor * c-c++-common/Warray-bounds-2.c: Declare helper static to avoid diff --git a/gcc/testsuite/gcc.dg/torture/pr84538.c b/gcc/testsuite/gcc.dg/torture/pr84538.c new file mode 100644 index 00000000000..b56a1c47176 --- /dev/null +++ b/gcc/testsuite/gcc.dg/torture/pr84538.c @@ -0,0 +1,16 @@ +/* { dg-do run } */ +/* { dg-additional-options "-fno-omit-frame-pointer -w" } */ + +#define SIZE 8 + +main() +{ + int a[SIZE] = {1}; + int i; + + for (i = 1; i < SIZE; i++) + if (a[i] != 0) + abort(); + + exit (0); +} -- 2.30.2