[gcc r12-3137] i386: Optimize lea with zero-extend. [PR 101716]

[gcc r12-3137] i386: Optimize lea with zero-extend. [PR 101716]

[Hongyu Wang]

https://gcc.gnu.org/g:87afc7b81cd44d04997add383856b2504af3afe6

commit r12-3137-g87afc7b81cd44d04997add383856b2504af3afe6
Author: Hongyu Wang <hongyu.wang@intel.com>
Date:   Tue Aug 17 16:53:46 2021 +0800

    i386: Optimize lea with zero-extend. [PR 101716]
    
    For ASHIFT + ZERO_EXTEND pattern, combine pass failed to
    match it to lea since it will generate non-canonical
    zero-extend. Adjust predicate and cost_model to allow combine
    for lea.
    
    gcc/ChangeLog:
    
            PR target/101716
            * config/i386/i386.c (ix86_live_on_entry): Adjust comment.
            (ix86_decompose_address): Remove retval check for ASHIFT,
            allow non-canonical zero extend if AND mask covers ASHIFT
            count.
            (ix86_legitimate_address_p): Adjust condition for decompose.
            (ix86_rtx_costs): Adjust cost for lea with non-canonical
            zero-extend.
    
            Co-Authored by: Uros Bizjak <ubizjak@gmail.com>
    
    gcc/testsuite/ChangeLog:
    
            PR target/101716
            * gcc.target/i386/pr101716.c: New test.

Diff:
---
 gcc/config/i386/i386.c                   | 36 ++++++++++++++++++++++++++------
 gcc/testsuite/gcc.target/i386/pr101716.c | 11 ++++++++++
 2 files changed, 41 insertions(+), 6 deletions(-)

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index ebec8668758..ddbbbceded1 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -10018,8 +10018,7 @@ ix86_live_on_entry (bitmap regs)
 \f
 /* Extract the parts of an RTL expression that is a valid memory address
    for an instruction.  Return 0 if the structure of the address is
-   grossly off.  Return -1 if the address contains ASHIFT, so it is not
-   strictly valid, but still used for computing length of lea instruction.  */
+   grossly off.  */
 
 int
 ix86_decompose_address (rtx addr, struct ix86_address *out)
@@ -10029,7 +10028,6 @@ ix86_decompose_address (rtx addr, struct ix86_address *out)
   HOST_WIDE_INT scale = 1;
   rtx scale_rtx = NULL_RTX;
   rtx tmp;
-  int retval = 1;
   addr_space_t seg = ADDR_SPACE_GENERIC;
 
   /* Allow zero-extended SImode addresses,
@@ -10053,6 +10051,27 @@ ix86_decompose_address (rtx addr, struct ix86_address *out)
 	  if (CONST_INT_P (addr))
 	    return 0;
 	}
+      else if (GET_CODE (addr) == AND)
+	{
+	  /* For ASHIFT inside AND, combine will not generate
+	     canonical zero-extend. Merge mask for AND and shift_count
+	     to check if it is canonical zero-extend.  */
+	  tmp = XEXP (addr, 0);
+	  rtx mask = XEXP (addr, 1);
+	  if (tmp && GET_CODE(tmp) == ASHIFT)
+	    {
+	      rtx shift_val = XEXP (tmp, 1);
+	      if (CONST_INT_P (mask) && CONST_INT_P (shift_val)
+		  && (((unsigned HOST_WIDE_INT) INTVAL(mask)
+		      | ((HOST_WIDE_INT_1U << INTVAL(shift_val)) - 1))
+		      == 0xffffffff))
+		{
+		  addr = lowpart_subreg (SImode, XEXP (addr, 0),
+					 DImode);
+		}
+	    }
+
+	}
     }
 
   /* Allow SImode subregs of DImode addresses,
@@ -10179,7 +10198,6 @@ ix86_decompose_address (rtx addr, struct ix86_address *out)
       if ((unsigned HOST_WIDE_INT) scale > 3)
 	return 0;
       scale = 1 << scale;
-      retval = -1;
     }
   else
     disp = addr;			/* displacement */
@@ -10252,7 +10270,7 @@ ix86_decompose_address (rtx addr, struct ix86_address *out)
   out->scale = scale;
   out->seg = seg;
 
-  return retval;
+  return 1;
 }
 \f
 /* Return cost of the memory address x.
@@ -10765,7 +10783,7 @@ ix86_legitimate_address_p (machine_mode, rtx addr, bool strict)
   HOST_WIDE_INT scale;
   addr_space_t seg;
 
-  if (ix86_decompose_address (addr, &parts) <= 0)
+  if (ix86_decompose_address (addr, &parts) == 0)
     /* Decomposition failed.  */
     return false;
 
@@ -20419,6 +20437,12 @@ ix86_rtx_costs (rtx x, machine_mode mode, int outer_code_i, int opno,
 	               << (GET_MODE (XEXP (x, 1)) != DImode)));
 	  return true;
 	}
+      else if (code == AND
+	       && address_no_seg_operand (x, mode))
+	{
+	  *total = cost->lea;
+	  return true;
+	}
       /* FALLTHRU */
 
     case NEG:
diff --git a/gcc/testsuite/gcc.target/i386/pr101716.c b/gcc/testsuite/gcc.target/i386/pr101716.c
new file mode 100644
index 00000000000..5e3ea64a320
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr101716.c
@@ -0,0 +1,11 @@
+/* PR target/101716 */
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-options "-O2" } */
+
+/* { dg-final { scan-assembler "leal\[\\t \]\[^\\n\]*eax" } } */
+/* { dg-final { scan-assembler-not "movl\[\\t \]\[^\\n\]*eax" } } */
+
+unsigned long long sample1(unsigned long long m) {
+    unsigned int t = -1;
+    return (m << 1) & t;
+}