[llvm] [X86] Remove redundant TEST after shifts when count is non-zero (PR #169069)

[Matt Arsenault via llvm-commits]

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@@ -386,3 +380,20 @@ define i32 @shl_var_self_select_amt_never_zero(i32 %a0, i32 %a1, i32 %a2, i32 %a
   %r = select i1 %c, i32 %s, i32 %a2
   ret i32 %r
 }
+
+define range(i8 0, 2) i8 @no_test_emitted_when_assume_shift_amt_gt_zero(i64 noundef %0, i32 noundef %1) {
+; CHECK-LABEL: no_test_emitted_when_assume_shift_amt_gt_zero:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movl %esi, %ecx
+; CHECK-NEXT:    # kill: def $cl killed $cl killed $ecx
+; CHECK-NEXT:    shlq %cl, %rdi
+; CHECK-NEXT:    sete %al
+; CHECK-NEXT:    retq
+  %3 = icmp sgt i32 %1, 0
+  tail call void @llvm.assume(i1 %3)
+  %4 = zext nneg i32 %1 to i64
+  %5 = shl i64 %0, %4
+  %6 = icmp eq i64 %5, 0
+  %7 = zext i1 %6 to i8
+  ret i8 %7
+}
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arsenm wrote:

Should have more examples, and some negative tests. In a more realistic scenario, I would hope the assume would have been dropped and turned into a range attribute on %1 

https://github.com/llvm/llvm-project/pull/169069