i386.md has

;; Convert imul by three, five and nine into lea
(define_peephole2
  [(parallel
    [(set (match_operand:SWI48 0 "register_operand" "")
          (mult:SWI48 (match_operand:SWI48 1 "register_operand" "")
                      (match_operand:SWI48 2 "const_int_operand" ""))) 
     (clobber (reg:CC FLAGS_REG))])]
  "INTVAL (operands[2]) == 3
   || INTVAL (operands[2]) == 5
   || INTVAL (operands[2]) == 9"
  [(set (match_dup 0)
        (plus:SWI48 (mult:SWI48 (match_dup 1) (match_dup 2))
                    (match_dup 1)))] 
  "operands[2] = GEN_INT (INTVAL (operands[2]) - 1);")

(define_peephole2
  [(parallel
    [(set (match_operand:SWI48 0 "register_operand" "")
          (mult:SWI48 (match_operand:SWI48 1 "nonimmediate_operand" "")
                      (match_operand:SWI48 2 "const_int_operand" ""))) 
     (clobber (reg:CC FLAGS_REG))])]
  "optimize_insn_for_speed_p ()
   && (INTVAL (operands[2]) == 3
       || INTVAL (operands[2]) == 5
       || INTVAL (operands[2]) == 9)"
  [(set (match_dup 0) (match_dup 1))
   (set (match_dup 0)
        (plus:SWI48 (mult:SWI48 (match_dup 0) (match_dup 2))
                    (match_dup 0)))]
  "operands[2] = GEN_INT (INTVAL (operands[2]) - 1);")


But lea split has

&& (!TARGET_PARTIAL_REG_STALL || optimize_function_for_size_p (cfun))

When TARGET_PARTIAL_REG_STALL is true, get got

[hjl@gnu-33 1036]$ cat x.i
 char *progName;
 int *tt;
 unsigned char *ll8;
 extern void foo (const char *);
 void cleanUpAndFail ( int ec ) {
    __builtin_exit ( ec );
 }
 void uncompressOutOfMemory ( int draw, int blockSize ) {
    foo ( "\tand failing that, find a machine with more memory.\n");
    cleanUpAndFail(1);
 }
 void setDecompressStructureSizes ( int newSize100k ) {
       int n = 100000 * newSize100k;
       ll8 = __builtin_malloc ( n * sizeof(unsigned char) );
       if (ll8 == ((void *)0) || tt == ((void *)0)) {
          int totalDraw             = n * sizeof(unsigned char) + n * sizeof(unsigned int);
          uncompressOutOfMemory ( totalDraw, n );
       }
 }
[hjl@gnu-33 1036]$ make x.s
/export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc -B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -O2  -S x.i
x.i: In function ‘setDecompressStructureSizes’:
x.i:19:2: error: unrecognizable insn:
(insn 43 19 21 4 (set (reg:SI 5 di [69])
        (plus:SI (mult:SI (reg/v:SI 3 bx [orig:59 n ] [59])
                (const_int 4 [0x4]))
            (reg/v:SI 3 bx [orig:59 n ] [59]))) x.i:16 -1
     (nil))
x.i:19:2: internal compiler error: in extract_insn, at recog.c:2113
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.
make: *** [x.s] Error 1
[hjl@gnu-33 1036]$