https://gcc.gnu.org/g:ac6d433b02ce26a646b2a7254b1d87fcc06b0beb
commit r15-3288-gac6d433b02ce26a646b2a7254b1d87fcc06b0beb
Author: Richard Sandiford <richard.sandif...@arm.com>
Date: Thu Aug 29 14:00:23 2024 +0100
Allow subregs around constant displacements [PR116516]
This patch fixes a regression introduced by g:708ee71808ea61758e73.
x86_64 allows addresses of the form:
(zero_extend:DI (subreg:SI (symbol_ref:DI "foo") 0))
Before the previous patch, a lax SUBREG check meant that we would
treat the subreg as a base and reload it into a base register.
But that wasn't what the target was expecting. Instead we should
treat "foo" as a constant displacement, to match:
leal foo, <dest>
After the patch, we recognised that "foo" isn't a base register,
but ICEd on it rather than handling it as a displacement.
With or without the recent patches, if the address had instead been:
(zero_extend:DI
(subreg:SI (plus:DI (reg:DI R) (symbol_ref:DI "foo") 0)))
then we would have treated "foo" as the displacement and R as the base
or index, as expected. The problem was that the code that does this was
rejecting all subregs of objects, rather than just subregs of variable
objects.
gcc/
PR middle-end/116516
* rtlanal.cc (strip_address_mutations): Allow subregs around
constant displacements.
gcc/testsuite/
PR middle-end/116516
* gcc.c-torture/compile/pr116516.c: New test.
Diff:
---
gcc/rtlanal.cc | 28 ++++++++++++++++++++++----
gcc/testsuite/gcc.c-torture/compile/pr116516.c | 10 +++++++++
2 files changed, 34 insertions(+), 4 deletions(-)
diff --git a/gcc/rtlanal.cc b/gcc/rtlanal.cc
index 8afbb32f2206..cb0c0c0d7197 100644
--- a/gcc/rtlanal.cc
+++ b/gcc/rtlanal.cc
@@ -6467,10 +6467,30 @@ strip_address_mutations (rtx *loc, enum rtx_code
*outer_code)
/* (and ... (const_int -X)) is used to align to X bytes. */
loc = &XEXP (*loc, 0);
else if (code == SUBREG
- && !OBJECT_P (SUBREG_REG (*loc))
- && subreg_lowpart_p (*loc))
- /* (subreg (operator ...) ...) inside and is used for mode
- conversion too. */
+ && (!OBJECT_P (SUBREG_REG (*loc))
+ || CONSTANT_P (SUBREG_REG (*loc)))
+ && subreg_lowpart_p (*loc))
+ /* (subreg (operator ...) ...) inside AND is used for mode
+ conversion too. It is also used for load-address operations
+ in which an extension can be done for free, such as:
+
+ (zero_extend:DI
+ (subreg:SI (plus:DI (reg:DI R) (symbol_ref:DI "foo") 0)))
+
+ The latter usage also covers subregs of plain "displacements",
+ such as:
+
+ (zero_extend:DI (subreg:SI (symbol_ref:DI "foo") 0))
+
+ The inner address should then be the symbol_ref, not the subreg,
+ similarly to the plus case above.
+
+ In contrast, the subreg in:
+
+ (zero_extend:DI (subreg:SI (reg:DI R) 0))
+
+ should be treated as the base, since it should be replaced by
+ an SImode hard register during register allocation. */
loc = &SUBREG_REG (*loc);
else
return loc;
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr116516.c
b/gcc/testsuite/gcc.c-torture/compile/pr116516.c
new file mode 100644
index 000000000000..c423ebfef5c0
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr116516.c
@@ -0,0 +1,10 @@
+extern void my_func (int);
+typedef struct {
+ int var;
+} info_t;
+extern void *_data_offs;
+void test()
+{
+ info_t *info = (info_t *) ((void *)((void *)1) + ((unsigned
int)&_data_offs));
+ my_func(info->var == 0);
+}
