In the gcc.target/aarch64/lsl_asr_sbfiz.c part of this PR, we have:
Failed to match this instruction:
(set (reg:SI 95)
(ashift:SI (subreg:SI (sign_extract:DI (subreg:DI (reg:SI 97) 0)
(const_int 3 [0x3])
(const_int 0 [0])) 0)
(const_int 19 [0x13])))
If we perform the natural simplification to:
(set (reg:SI 95)
(ashift:SI (sign_extract:SI (reg:SI 97)
(const_int 3 [0x3])
(const_int 0 [0])) 0)
(const_int 19 [0x13])))
then the pattern matches. And it turns out that we do have a
simplification like that already, but it would only kick in for
extractions from a reg, not a subreg. E.g.:
(set (reg:SI 95)
(ashift:SI (subreg:SI (sign_extract:DI (reg:DI X)
(const_int 3 [0x3])
(const_int 0 [0])) 0)
(const_int 19 [0x13])))
would simplify to:
(set (reg:SI 95)
(ashift:SI (sign_extract:SI (subreg:SI (reg:DI X) 0)
(const_int 3 [0x3])
(const_int 0 [0])) 0)
(const_int 19 [0x13])))
IMO the subreg case is even more obviously a simplification
than the bare reg case, since the net effect is to remove
either one or two subregs, rather than simply change the
position of a subreg/truncation.
However, doing that regressed gcc.dg/tree-ssa/pr64910-2.c
for -m32 on x86_64-linux-gnu, because we could then simplify
a :HI zero_extract to a :QI one. The associated *testqi_ext_3
pattern did already seem to want to handle QImode extractions:
"ix86_match_ccmode (insn, CCNOmode)
&& ((TARGET_64BIT && GET_MODE (operands[2]) == DImode)
|| GET_MODE (operands[2]) == SImode
|| GET_MODE (operands[2]) == HImode
|| GET_MODE (operands[2]) == QImode)
but I'm not sure how often the QI case would trigger in practice,
since the zero_extract mode was restricted to HI and above. I checked
the other x86 patterns and couldn't see any other instances of this.
Tested on aarch64-linux-gnu, x86_64-linux-gnu and powerpc64le-linux-gnu,
OK to install?
Richard
2020-01-27 Richard Sandiford <richard.sandif...@arm.com>
gcc/
PR rtl-optimization/87763
* simplify-rtx.c (simplify_truncation): Extend sign/zero_extract
simplification to handle subregs as well as bare regs.
* config/i386/i386.md (*testqi_ext_3): Match QI extracts too.
---
gcc/config/i386/i386.md | 2 +-
gcc/simplify-rtx.c | 4 +++-
2 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 6e9c9bd2fb6..a125ab350bb 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -8927,7 +8927,7 @@ (define_insn "*testqi_ext_2"
(define_insn_and_split "*testqi_ext_3"
[(set (match_operand 0 "flags_reg_operand")
(match_operator 1 "compare_operator"
- [(zero_extract:SWI248
+ [(zero_extract:SWI
(match_operand 2 "nonimmediate_operand" "rm")
(match_operand 3 "const_int_operand" "n")
(match_operand 4 "const_int_operand" "n"))
diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index eff1d07a253..db4f9339c15 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -736,7 +736,9 @@ simplify_truncation (machine_mode mode, rtx op,
(*_extract:M1 (truncate:M1 (reg:M2)) (len) (pos')) if possible without
changing len. */
if ((GET_CODE (op) == ZERO_EXTRACT || GET_CODE (op) == SIGN_EXTRACT)
- && REG_P (XEXP (op, 0))
+ && (REG_P (XEXP (op, 0))
+ || (SUBREG_P (XEXP (op, 0))
+ && REG_P (SUBREG_REG (XEXP (op, 0)))))
&& GET_MODE (XEXP (op, 0)) == GET_MODE (op)
&& CONST_INT_P (XEXP (op, 1))
&& CONST_INT_P (XEXP (op, 2)))
--
2.17.1
