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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122217 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86InstrCompiler.td b/lib/Target/X86/X86InstrCompiler.td
index 724e6b895e4fc77045268a1dc56728886cb8760e..da5e05a5d7ef7b87eed9a302cdfdabb80f3d5c6d 100644 (file)
--- a/lib/Target/X86/X86InstrCompiler.td
+++ b/lib/Target/X86/X86InstrCompiler.td
@@ -207,6 +207,12 @@ def : Pat<(i32 (sext (i8 (X86setcc_c X86_COND_B, EFLAGS)))),
 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

diff --git a/test/CodeGen/X86/add.ll b/test/CodeGen/X86/add.ll
index 3991a6849f3ed3d1d2f5601eacc86fa585173b88..1201c06fcce1539527c8c6450d26ded099938580 100644 (file)
--- a/test/CodeGen/X86/add.ll
+++ b/test/CodeGen/X86/add.ll
@@ -92,3 +92,12 @@ define i64 @test6(i64 %A, i32 %B) nounwind {
 ; X64: ret
 }
 
+define {i32, i1} @test7(i32 %v1, i32 %v2) nounwind {
+   %t = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %v1, i32 %v2)
+   ret {i32, i1} %t
+}
+
+; X64: test7:
+; X64: addl %esi, %eax
+; X64-NEXT: setb %dl
+; X64-NEXT: ret