RE: [x86 PATCH] PR target/31985: Improve memory operand use with doubleword add.

["Roger Sayle" <roger@nextmovesoftware.com>]

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Hi Uros,

> On the 7th June 2023, Uros Bizkak wrote:
> The register allocator considers the instruction-to-be-split as one instruction, so it
> can allocate output register to match an input register (or a register that forms an
> input address), So, you have to either add an early clobber to the output, or
> somehow prevent output to clobber registers in the second pattern.

This implements your suggestion of adding an early clobber to the output, a
one character ('&') change from the previous version of this patch.  Retested
with make bootstrap and make -k check, with and without -m32, to confirm
there are no issues, and this still fixes the pr31985.c test case.

As you've suggested, I'm also working on improving STV in this area.

Ok for mainline?


2023-06-15  Roger Sayle  <roger@nextmovesoftware.com>
            Uros Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog
        PR target/31985
        * config/i386/i386.md (*add<dwi>3_doubleword_concat): New
        define_insn_and_split combine *add<dwi>3_doubleword with a
        *concat<mode><dwi>3 for more efficient lowering after reload.

gcc/testsuite/ChangeLog
        PR target/31985
        * gcc.target/i386/pr31985.c: New test case.

Roger
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diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index e6ebc46..42c302d 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -6124,6 +6124,36 @@
 	      (clobber (reg:CC FLAGS_REG))])]
  "split_double_mode (<DWI>mode, &operands[0], 2, &operands[0], &operands[3]);")
 
+(define_insn_and_split "*add<dwi>3_doubleword_concat"
+  [(set (match_operand:<DWI> 0 "register_operand" "=&r")
+	(plus:<DWI>
+	  (any_or_plus:<DWI>
+	    (ashift:<DWI>
+	      (zero_extend:<DWI>
+		(match_operand:DWIH 2 "nonimmediate_operand" "rm"))
+	      (match_operand:<DWI> 3 "const_int_operand"))
+	    (zero_extend:<DWI>
+	      (match_operand:DWIH 4 "nonimmediate_operand" "rm")))
+	  (match_operand:<DWI> 1 "register_operand" "0")))
+   (clobber (reg:CC FLAGS_REG))]
+  "INTVAL (operands[3]) == <MODE_SIZE> * BITS_PER_UNIT"
+  "#"
+  "&& reload_completed"
+  [(parallel [(set (reg:CCC FLAGS_REG)
+		   (compare:CCC
+		     (plus:DWIH (match_dup 1) (match_dup 4))
+		     (match_dup 1)))
+	      (set (match_dup 0)
+		   (plus:DWIH (match_dup 1) (match_dup 4)))])
+   (parallel [(set (match_dup 5)
+		   (plus:DWIH
+		     (plus:DWIH
+		       (ltu:DWIH (reg:CC FLAGS_REG) (const_int 0))
+		       (match_dup 6))
+		     (match_dup 2)))
+	      (clobber (reg:CC FLAGS_REG))])]
+ "split_double_mode (<DWI>mode, &operands[0], 2, &operands[0], &operands[5]);")
+
 (define_insn "*add<mode>_1"
   [(set (match_operand:SWI48 0 "nonimmediate_operand" "=rm,r,r,r")
 	(plus:SWI48
diff --git a/gcc/testsuite/gcc.target/i386/pr31985.c b/gcc/testsuite/gcc.target/i386/pr31985.c
new file mode 100644
index 0000000..a6de1b5
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr31985.c
@@ -0,0 +1,14 @@
+/* { dg-do compile { target ia32 } } */
+/* { dg-options "-O2" } */
+
+void test_c (unsigned int a, unsigned int b, unsigned int c, unsigned int d)
+{
+  volatile unsigned int x, y;
+  unsigned long long __a = b | ((unsigned long long)a << 32);
+  unsigned long long __b = d | ((unsigned long long)c << 32);
+  unsigned long long __c = __a + __b;
+  x = (unsigned int)(__c & 0xffffffff);
+  y = (unsigned int)(__c >> 32);
+}
+
+/* { dg-final { scan-assembler-times "movl" 4 } } */