[InstCombine] narrow truncated add/sub/mul with constant
Name: narrow_sub
%sub = sub i32 C1, %x
%r = trunc i32 %sub to i8
=>
%xn = trunc i32 %x to i8
%narrowC = trunc i32 C1 to i8
%r = sub i8 %narrowC, %xn
Name: narrow_add
%add = add i32 %x, C1
%r = trunc i32 %add to i8
=>
%xn = trunc i32 %x to i8
%narrowC = trunc i32 C1 to i8
%r = add i8 %xn, %narrowC
Name: narrow_mul
%mul = mul i32 %x, C1
%r = trunc i32 %mul to i8
=>
%xn = trunc i32 %x to i8
%narrowC = trunc i32 C1 to i8
%r = mul i8 %xn, %narrowC
http://rise4fun.com/Alive/QpS
This doesn't solve PR34046 (failure to recognize rotate):
https://bugs.llvm.org/show_bug.cgi?id=34046
...but it reduces an extra complication in the description examples
to a form that we can more easily match.
llvm-svn: 310141
diff --git a/llvm/test/Transforms/InstCombine/fls.ll b/llvm/test/Transforms/InstCombine/fls.ll
index 75a3520..bf87e6a 100644
--- a/llvm/test/Transforms/InstCombine/fls.ll
+++ b/llvm/test/Transforms/InstCombine/fls.ll
@@ -31,8 +31,8 @@
define i32 @flsnotconst(i64 %z) {
; CHECK-LABEL: @flsnotconst(
; CHECK-NEXT: [[CTLZ:%.*]] = call i64 @llvm.ctlz.i64(i64 %z, i1 false), !range !0
-; CHECK-NEXT: [[TMP1:%.*]] = sub nsw i64 64, [[CTLZ]]
-; CHECK-NEXT: [[TMP2:%.*]] = trunc i64 [[TMP1]] to i32
+; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[CTLZ]] to i32
+; CHECK-NEXT: [[TMP2:%.*]] = sub nsw i32 64, [[TMP1]]
; CHECK-NEXT: ret i32 [[TMP2]]
;
%goo = call i32 @flsl(i64 %z)