(ffssi2, ffshi2): Assume bsf produces garbage if input is 0.

(ffssi2, ffshi2): Assume bsf produces
garbage if input is 0.  Use jumps to load output in that case.

From-SVN: r4911

gcc/config/i386/i386.md

@@ -4460,12 +4460,17 @@
   ""
   "*
 {
-  rtx xops[2];
+  rtx xops[3];
 
   xops[0] = operands[0];
-  xops[1] = constm1_rtx;
-  output_asm_insn (AS2 (mov%L0,%1,%0), xops);
-  return AS2 (bsf%L0,%1,%0);
+  xops[1] = operands[1];
+  xops[2] = constm1_rtx;
+  /* Can there be a way to avoid the jump here?  */
+  output_asm_insn (AS2 (bsf%L0,%1,%0), xops);
+  output_asm_insn (\"jnz 1f\", xops);
+  output_asm_insn (AS2 (mov%L0,%2,%0), xops);
+  output_asm_insn (\"1:\", xops);
+  return \"\";
 }")
 
 (define_expand "ffshi2"
@@ -4484,12 +4489,16 @@
   ""
   "*
 {
-  rtx xops[2];
+  rtx xops[3];
 
   xops[0] = operands[0];
-  xops[1] = constm1_rtx;
-  output_asm_insn (AS2 (mov%W0,%1,%0), xops);
-  return AS2 (bsf%W0,%1,%0);
+  xops[1] = operands[1];
+  xops[2] = constm1_rtx;
+  output_asm_insn (AS2 (bsf%W0,%1,%0), xops);
+  output_asm_insn (\"jnz 1f\", xops);
+  output_asm_insn (AS2 (mov%W0,%2,%0), xops);
+  output_asm_insn (\"1:\", xops);
+  return \"\";
 }")
 
 ;; These patterns match the binary 387 instructions for addM3, subM3,