We lower setb to sbb with the hope that the and will go away, when it
doesn't, match it back to setb.
On a 64-bit version of the testcase before we'd get:
movq %rdi, %rax
addq %rsi, %rax
sbbb %dl, %dl
andb $1, %dl
ret
now we get:
movq %rdi, %rax
addq %rsi, %rax
setb %dl
ret
llvm-svn: 122217
diff --git a/llvm/lib/Target/X86/X86InstrCompiler.td b/llvm/lib/Target/X86/X86InstrCompiler.td
index 724e6b8..da5e05a 100644
--- a/llvm/lib/Target/X86/X86InstrCompiler.td
+++ b/llvm/lib/Target/X86/X86InstrCompiler.td
@@ -207,6 +207,12 @@
def : Pat<(i64 (sext (i8 (X86setcc_c X86_COND_B, EFLAGS)))),
(SETB_C64r)>;
+// We canonicalize 'setb' to "(and (sbb reg,reg), 1)" on the hope that the and
+// will be eliminated and that the sbb can be extended up to a wider type. When
+// this happens, it is great. However, if we are left with an 8-bit sbb and an
+// and, we might as well just match it as a setb.
+def : Pat<(and (i8 (X86setcc_c X86_COND_B, EFLAGS)), 1),
+ (SETBr)>;
//===----------------------------------------------------------------------===//
// String Pseudo Instructions