InstCombine: Turn icmp + sext into bitwise/integer ops when the input has only one unknown bit.

int test1(unsigned x) { return (x&8) ? 0 : -1; }
int test3(unsigned x) { return (x&8) ? -1 : 0; }

before (x86_64):
_test1:
	andl	$8, %edi
	cmpl	$1, %edi
	sbbl	%eax, %eax
	ret
_test3:
	andl	$8, %edi
	cmpl	$1, %edi
	sbbl	%eax, %eax
	notl	%eax
	ret

after:
_test1:
	shrl	$3, %edi
	andl	$1, %edi
	leal	-1(%rdi), %eax
	ret
_test3:
	shll	$28, %edi
	movl	%edi, %eax
	sarl	$31, %eax
	ret

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128732 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 48 insertions, 0 deletions

diff --git a/test/Transforms/InstCombine/sext.ll b/test/Transforms/InstCombine/sext.ll
index da52d92..f49a2ef 100644
--- a/test/Transforms/InstCombine/sext.ll
+++ b/test/Transforms/InstCombine/sext.ll
@@ -136,3 +136,51 @@ define i64 @test12(i32 %x) nounwind {
 ; CHECK: sext
 ; CHECK: ret
 }
+
+define i32 @test13(i32 %x) nounwind {
+  %and = and i32 %x, 8
+  %cmp = icmp eq i32 %and, 0
+  %ext = sext i1 %cmp to i32
+  ret i32 %ext
+; CHECK: @test13
+; CHECK-NEXT: %and = lshr i32 %x, 3
+; CHECK-NEXT: %1 = and i32 %and, 1
+; CHECK-NEXT: %sext = add i32 %1, -1
+; CHECK-NEXT: ret i32 %sext
+}
+
+define i32 @test14(i16 %x) nounwind {
+  %and = and i16 %x, 16
+  %cmp = icmp ne i16 %and, 16
+  %ext = sext i1 %cmp to i32
+  ret i32 %ext
+; CHECK: @test14
+; CHECK-NEXT: %and = lshr i16 %x, 4
+; CHECK-NEXT: %1 = and i16 %and, 1
+; CHECK-NEXT: %sext = add i16 %1, -1
+; CHECK-NEXT: %ext = sext i16 %sext to i32
+; CHECK-NEXT: ret i32 %ext
+}
+
+define i32 @test15(i32 %x) nounwind {
+  %and = and i32 %x, 16
+  %cmp = icmp ne i32 %and, 0
+  %ext = sext i1 %cmp to i32
+  ret i32 %ext
+; CHECK: @test15
+; CHECK-NEXT: %1 = shl i32 %x, 27
+; CHECK-NEXT: %sext = ashr i32 %1, 31
+; CHECK-NEXT: ret i32 %sext
+}
+
+define i32 @test16(i16 %x) nounwind {
+  %and = and i16 %x, 8
+  %cmp = icmp eq i16 %and, 8
+  %ext = sext i1 %cmp to i32
+  ret i32 %ext
+; CHECK: @test16
+; CHECK-NEXT: %1 = shl i16 %x, 12
+; CHECK-NEXT: %sext = ashr i16 %1, 15
+; CHECK-NEXT: %ext = sext i16 %sext to i32
+; CHECK-NEXT: ret i32 %ext
+}