[InstCombine] Add test cases to show missed opportunities to remove compare instructions after cttz/ctlz/ctpop where some bits of the input is known.

llvm-svn: 304224

2 files changed, 44 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/ctpop.ll b/llvm/test/Transforms/InstCombine/ctpop.ll
index 6bc6f973197..d49a907ffce 100644
--- a/llvm/test/Transforms/InstCombine/ctpop.ll
+++ b/llvm/test/Transforms/InstCombine/ctpop.ll
@@ -52,3 +52,19 @@ define i1 @test4(i8 %arg) {
   %res = icmp eq i8 %cnt, 2
   ret i1 %res
 }
+
+; Test when the number of possible known bits isn't one less than a power of 2
+; and the compare value is greater but less than the next power of 2.
+; TODO: The icmp is unnecessary given the known bits of the input.
+define i1 @test5(i32 %arg) {
+; CHECK-LABEL: @test5(
+; CHECK-NEXT:    [[AND:%.*]] = and i32 [[ARG:%.*]], 3
+; CHECK-NEXT:    [[CNT:%.*]] = call i32 @llvm.ctpop.i32(i32 [[AND]])
+; CHECK-NEXT:    [[RES:%.*]] = icmp eq i32 [[CNT]], 3
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %and = and i32 %arg, 3
+  %cnt = call i32 @llvm.ctpop.i32(i32 %and)
+  %res = icmp eq i32 %cnt, 3
+  ret i1 %res
+}
diff --git a/llvm/test/Transforms/InstCombine/intrinsics.ll b/llvm/test/Transforms/InstCombine/intrinsics.ll
index 5654b265da5..78c98955353 100644
--- a/llvm/test/Transforms/InstCombine/intrinsics.ll
+++ b/llvm/test/Transforms/InstCombine/intrinsics.ll
@@ -305,6 +305,20 @@ define i1 @cttz_knownbits2(i32 %arg) {
   ret i1 %res
 }
 
+; TODO: The icmp is unnecessary given the known bits of the input.
+define i1 @cttz_knownbits3(i32 %arg) {
+; CHECK-LABEL: @cttz_knownbits3(
+; CHECK-NEXT:    [[OR:%.*]] = or i32 [[ARG:%.*]], 4
+; CHECK-NEXT:    [[CNT:%.*]] = call i32 @llvm.cttz.i32(i32 [[OR]], i1 true) #2
+; CHECK-NEXT:    [[RES:%.*]] = icmp eq i32 [[CNT]], 3
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %or = or i32 %arg, 4
+  %cnt = call i32 @llvm.cttz.i32(i32 %or, i1 true) nounwind readnone
+  %res = icmp eq i32 %cnt, 3
+  ret i1 %res
+}
+
 define i8 @ctlz(i8 %a) {
 ; CHECK-LABEL: @ctlz(
 ; CHECK-NEXT:    ret i8 2
@@ -338,6 +352,20 @@ define i1 @ctlz_knownbits2(i8 %arg) {
   ret i1 %res
 }
 
+; TODO: The icmp is unnecessary given the known bits of the input.
+define i1 @ctlz_knownbits3(i8 %arg) {
+; CHECK-LABEL: @ctlz_knownbits3(
+; CHECK-NEXT:    [[OR:%.*]] = or i8 [[ARG:%.*]], 32
+; CHECK-NEXT:    [[CNT:%.*]] = call i8 @llvm.ctlz.i8(i8 [[OR]], i1 true) #2
+; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[CNT]], 3
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %or = or i8 %arg, 32
+  %cnt = call i8 @llvm.ctlz.i8(i8 %or, i1 true) nounwind readnone
+  %res = icmp eq i8 %cnt, 3
+  ret i1 %res
+}
+
 define void @cmp.simplify(i32 %a, i32 %b, i1* %c) {
   %lz = tail call i32 @llvm.ctlz.i32(i32 %a, i1 false) nounwind readnone
   %lz.cmp = icmp eq i32 %lz, 32