[gcc(refs/vendors/redhat/heads/gcc-10-branch)] simplify-rtx: Extend (truncate (*extract ...)) fold [PR87763]

[Jakub Jelinek]

https://gcc.gnu.org/g:465c7c89e92a6d6d582173e505cb16dcb9873034

commit 465c7c89e92a6d6d582173e505cb16dcb9873034
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Sun Jan 26 13:01:48 2020 +0000

    simplify-rtx: Extend (truncate (*extract ...)) fold [PR87763]
    
    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.
    
    2020-01-28  Richard Sandiford  <richard.sandiford@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.

Diff:
---
 gcc/ChangeLog           | 7 +++++++
 gcc/config/i386/i386.md | 2 +-
 gcc/simplify-rtx.c      | 4 +++-
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 4d6ceb6..9fc93c9 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,12 @@
 2020-01-28  Richard Sandiford  <richard.sandiford@arm.com>
 
+	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.
+
+2020-01-28  Richard Sandiford  <richard.sandiford@arm.com>
+
 	* tree-vect-loop.c (vectorizable_reduction): Fail gracefully
 	for reduction chains that (now) include a call.
 
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 6e9c9bd..a125ab3 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -8927,7 +8927,7 @@
 (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 eff1d07..db4f933 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)))