On 2/22/24 2:08 PM, Jakub Jelinek wrote:
On Thu, Feb 22, 2024 at 12:59:18PM -0800, Greg McGary wrote:
The sign bit of a sign-extending load cannot be known until runtime,
so don't attempt to simplify it in the combiner.
2024-02-22 Greg McGary <g...@rivosinc.com>
PR rtl-optimization/113010
* combine.cc (simplify_comparison): Don't simplify high part
of paradoxical-SUBREG-of-MEM on machines that sign-extend loads
* gcc.c-torture/execute/pr113010.c: New test.
---
gcc/combine.cc | 10 ++++++++--
gcc/testsuite/gcc.c-torture/execute/pr113010.c | 9 +++++++++
2 files changed, 17 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr113010.c
diff --git a/gcc/combine.cc b/gcc/combine.cc
index 812553c091e..736206242e1 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -12550,9 +12550,15 @@ simplify_comparison (enum rtx_code code, rtx *pop0,
rtx *pop1)
}
/* If the inner mode is narrower and we are extracting the low part,
- we can treat the SUBREG as if it were a ZERO_EXTEND. */
+ we can treat the SUBREG as if it were a ZERO_EXTEND ... */
if (paradoxical_subreg_p (op0))
- ;
+ {
+ /* ... except we can't treat as ZERO_EXTEND when a machine
+ automatically sign-extends loads. */
+ if (MEM_P (SUBREG_REG (op0)) && WORD_REGISTER_OPERATIONS
+ && load_extend_op (inner_mode) == SIGN_EXTEND)
+ break;
That doesn't feel sufficient. Like in the PR112758 patch, I believe
for WORD_REGISTER_OPERATIONS you should treat it as a ZERO_EXTEND only
if MEM_P (SUBREG_REG (op0)) && load_extend_op (inner_mode) == ZERO_EXTEND
or if GET_MODE_PRECISION (inner_mode) is known to be >= BITS_PER_WORD.
Jakub
The gist of your comment is that my patch was missing the test for width
of inner_mode vs. BITS_PER_WORD. Here's a revision. Looks good to you?
diff --git a/gcc/combine.cc b/gcc/combine.cc
index 812553c091e..4626f2edae9 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -12550,9 +12550,17 @@ simplify_comparison (enum rtx_code code, rtx
*pop0, rtx *pop1)
}
/* If the inner mode is narrower and we are extracting the
low part,
- we can treat the SUBREG as if it were a ZERO_EXTEND. */
+ we can treat the SUBREG as if it were a ZERO_EXTEND ... */
if (paradoxical_subreg_p (op0))
- ;
+ {
+ /* ... except we can't do that for loads on machines
+ that don't automatically zero-extend loads. */
+ if (WORD_REGISTER_OPERATIONS
+ && GET_MODE_PRECISION (inner_mode) < BITS_PER_WORD
+ && MEM_P (SUBREG_REG (op0))
+ && load_extend_op (inner_mode) != ZERO_EXTEND)
+ break;
+ }
else if (subreg_lowpart_p (op0)
&& GET_MODE_CLASS (mode) == MODE_INT
&& is_int_mode (GET_MODE (SUBREG_REG (op0)),
&inner_mode)
