DAGCombine add (sext i1), X into sub X, (zext i1) if sext from i1 is illegal. The latter usually compiles into smaller code.
example code:
unsigned foo(unsigned x, unsigned y) {
if (x != 0) y--;
return y;
}
before:
_foo: ## @foo
cmpl $1, 4(%esp) ## encoding: [0x83,0x7c,0x24,0x04,0x01]
sbbl %eax, %eax ## encoding: [0x19,0xc0]
notl %eax ## encoding: [0xf7,0xd0]
addl 8(%esp), %eax ## encoding: [0x03,0x44,0x24,0x08]
ret ## encoding: [0xc3]
after:
_foo: ## @foo
cmpl $1, 4(%esp) ## encoding: [0x83,0x7c,0x24,0x04,0x01]
movl 8(%esp), %eax ## encoding: [0x8b,0x44,0x24,0x08]
adcl $-1, %eax ## encoding: [0x83,0xd0,0xff]
ret ## encoding: [0xc3]
llvm-svn: 122455
1f4dfbbcb0